nena masthead
SENA Home Staff & Editors For Readers For Authors

Agonistic Interactions Among Size-matched Form I and Form II Male Procambarus suttkusi (Choctawhatchee Crayfish)
Paul M. Stewart, Amanda D. McKenzie, Thomas P. Simon, and Amanda M. Baker

Southeastern Naturalist, Volume 9, Special Issue 3 (2010): 231–244

Full-text pdf (Accessible only to subscribers.To subscribe click here.)

 



Access Journal Content

Open access browsing of table of contents and abstract pages. Full text pdfs available for download for subscribers.

Issue-in-Progress: Vol. 23 (1) ... early view

Current Issue: Vol. 22 (3)
SENA 22(3)

Check out SENA's latest Special Issue:

Special Issue 12
SENA 22(special issue 12)

All Regular Issues

Monographs

Special Issues

 

submit

 

subscribe

 

JSTOR logoClarivate logoWeb of science logoBioOne logo EbscoHOST logoProQuest logo


Conservation, Biology, and Natural History of Crayfishes from the Southern US 2010 Southeastern Naturalist 9(Special Issue 3):231–244 Agonistic Interactions Among Size-matched Form I and Form II Male Procambarus suttkusi (Choctawhatchee Crayfish) Paul M. Stewart1,*, Amanda D. McKenzie1, Thomas P. Simon2, and Amanda M. Baker1 Abstract - This study observed agonistic interactions and contests between sizematched form I vs. form I, form II vs. form II, and form I vs. form II males to establish baseline dominance orders and behavioral dynamics for Procambarus suttkusi (Choctawhatchee Crayfish). Three types of initiation behaviors, or attacks, were observed during each interaction: ambivalent contact, claw raise, and lunge. Feeding competition studies were also performed to assess the relationship between the winners of the agonistic interactions and feeding contests. Only form I vs. form I contests showed a decline in the number of interactions observed over time, but the duration of each individual agonistic interaction declined for all three types of behaviors during the thirty-minute recording period. Winners and losers did not preferentially use the same initiation behaviors as used in other studies. Previous studies also documented form I dominating form II males, but form I males did not dominate form II males in the present study. Winners of the agonistic contests won significantly more feeding contests. The results of the current study suggested that behavioral dynamics and form dominance may be species specific and that careful consideration of size differences are necessary in order to examine form dominance. Introduction Aggressive behaviors are important to many organisms (Lowe 1956) and have been studied extensively in crustaceans, including lobsters (Karavanich and Atema 1998, Karnofsky et al. 1989), crabs (Hazlett 1997), prawns (Barki et al. 1992, Evans and Shehadi-Moacdieh 1988), and crayfish (Capelli and Hamilton 1984, Hazlett et al. 1992, Quinn and Janssen 1989). Crustaceans compete for resources using aggressive interactions, often termed agonistic interactions. As a result of these behaviors, hierarchical relationships are thought to be formed (Copp 1986, Issa et al. 1999), giving the organism with the higher rank access to the best resources, such as shelter, reproductive success, and feeding access (Klocker and Strayer 2004, Krebs and Davies 1987). The subordinate organism is often excluded from these resources, especially when resources are limited (Edsman and Jonsson 1996, Söderbäck 1991). Hierarchical relationships begin to form when two crayfish first encounter each other and exhibit intricate, stereotyped behavior, usually escalating into an agonistic interaction (May and Mercier 2006, Tierney et al. 2000). 1Department of Biological and Environmental Sciences, Troy University, Troy, AL 36081. 22364 East Linden Hill Drive, Bloomington, IN 47401. *Corresponding author - mstewart@troy.edu. 232 Southeastern Naturalist Vol. 9, Special Issue 3 Interactions occur with and without the presence of resources (Issa et al. 1999). As dominance orders become established, the intensity and frequency of agonistic competitions decrease as one of the competitors avoids the other and exhibits submissive instead of dominant behaviors (Gherardi and Daniels 2003, Herberholz et al. 2003). This sequence of behaviors signifies the establishment of dominance order (Herberholz et al. 2003). Visual communication, such as claw and antennae postures, and physical contact are major aspects of agonistic interactions and are important in determining the intensity of subsequent contests (Baird et al. 2006, Smith and Dunham 1990). Agonistic interactions between pairs of crayfish involve threat behaviors such as attacks and chelae interactions and avoidance behaviors such as walking away and tailflips (Lundberg 2004). The attacks, often called initiation behaviors, were further divided by Guiasu and Dunham (1997b, 1998, 1999) into categories of ambivalent contact, claw raise, and lunge. The claw raise and the lunge are more aggressive behaviors, and the ambivalent contact and avoidance behaviors are submissive behaviors (Guiasu and Dunham 1997b, 1998, 1999; Issa et al. 1999). The intensity and extent with which a particular agonistic behavior is used differs among crayfish species (Tierney et al. 2000). Asymmetrical morphological differences between two opponents often influence success in interactions (Barki et al. 1992, Rubenstein and Hazlett 1974). Asymmetric contests are shorter and less intense, with larger individuals winning agonistic contests and gaining access to more advantageous resources (Bergman and Moore 2003). For example, chelae size is important to the aggressive strategies of crayfish (Schroeder and Huber 2001). Orconectes rusticus (Girard) (Rusty Crayfish) with larger chelae usually win intraspecific interactions (Gherardi et al. 2000, Snedden 1990). However, size-matched opponents have longer agonistic interactions (Bergman and Moore 2003). Reproductive morphology may also influence the outcomes of agonistic interactions. Form I males are reproductively active and usually have a larger carapace to chelae size ratio than non-reproductively active form II males (Stein 1976). Some species have a synchronous alternation between reproductive forms (Orconectes species) and other species (Cambarus species) molt and breed many times of the year (Guiasu and Dunham 1998). Procambarus suttkusi Hobbs (Choctawhatchee Crayfish) has a synchronous reproductive cycle, from May to September, but form II males of reproductive size can be found in the population during the mating period (Baker et al. 2008). During this time, form I males may compete with form II males for valuable stream resources. Guiasu and Dunham (1998) suggested that form I males dominate form II males. Extrinsic asymmetries also influence agonistic interactions. These include previous wins in agonistic contests, prior residence when competing for shelters, and differences in fight strategies (Bergman and Moore 2003). For example, winners of previous interactions behave in the same manner as in preceding contests when competing with familiar and unfamiliar 2010 P.M. Stewart, A.D. McKenzie, T.P. Simon, and A.M. Baker 233 opponents, thus increasing the likelihood of successive wins or successive losses (Bergman et al. 2003, Gherardi and Daniels 2003). The effects of extrinsic asymmetries are time dependent, variable, and frequently species specific (Bergman et al. 2003). Many studies have documented aggressive behaviors in crayfish (Figler et al. 1999, Guiasu and Dunham 1998, Rorer and Capelli 1978), but no studies have focused on species that are indigenous to the southeastern coastal plains ecoregion of the United States. The subject of this study was Procambarus suttkusi, a species widely distributed and dominant in the Choctawhatchee drainage system of Alabama and northern Florida (Heath et al. 2010, Hobbs 1953) where, because of its limited range, it has been listed as a species of concern (Bouchard 1976, Fitzpatrick 1990). Form I and form II individuals co-exist temporally in the Choctawhatchee watershed, but information for P. suttkusi is limited, and the dominance order among reproductive forms of male P. suttkusi has not been documented. The current study analyzed agonistic interactions between form I vs. form I, form II vs. form II, and form I vs. form II P. suttkusi males to establish baseline dominance orders and agonistic dynamics for this species. Three types of initiation behaviors, including lunge, claw raise, and ambivalent contact, demonstrated by the winners and losers of each individual interaction were quantified. These same pairs of individuals competed for food in another trial to see if the winners of the agonistic contests would also win the feeding contests. These data may be used to compare the agonistic behaviors of this species to others to better understand competitive exclusion mechanisms. Methods Collection sites Crayfish were collected from wadeable streams of the Choctawhatchee watershed, previously known to contain P. suttkusi (Heath et al. 2010). All streams sampled in the current study were moderately meandering streams that have not been channelized or dredged, except for Persimmon Branch. The low-gradient, wadeable streams of this watershed are characterized by sandy substrates, woody debris, leaf packs, root wads, and instream vegetation. Laboratory preparations Form I and form II P. suttkusi males were collected using wire minnow baskets and a Smith Root Model 12-B ® backpack electrofisher. Identifications were confirmed in the Troy University laboratory using taxonomic keys (Hobbs 1981). Each crayfish, after being kept dry for two minutes, was weighed to the nearest tenth of a gram. Using digital calipers, the cephalothorax length and the length and width of the largest chelae were measured for each crayfish. Sixteen form I vs. form I, 20 form II vs. form II, and 13 form I vs. form II male pairs were size-matched, and each form I vs. form I and form II vs. form II pair differed by no more than 2 grams in body weight and a 10% difference in chelae length (Nakata and Goshima 2003, Tierney et al. 2000). 234 Southeastern Naturalist Vol. 9, Special Issue 3 Form I vs. form II pairs were size-matched in order to eliminate the effects of size advantage on the outcome of the agonistic contests and differed by no more than a 10% difference in chelae length. Numbers were placed on each pair using correction fluid. Each crayfish was held in an isolated area of the holding tank for at least one week in preparation for the agonistic contest to reduce the impacts of any previous interactions (Gherardi and Daniels 2003). The isolated areas of the holding tank for each crayfish consisted of a 10.2-cm diameter, 15.5-cm long PVC pipe. The PVC pipe was covered by a wire mesh material, with an aeration stone placed in the middle of the holding area. To reduce the effects of hunger on motivational differences, crayfish were last fed Lumbricus sp. (night crawler) pieces 24 hours prior to the agonistic contest. The experimental tank, 51 cm (length) x 25 cm (width) x 29 cm (height), was divided into two equal halves using a vinyl plexiglass divider and contained gravel substrate, about 3 cm in depth. All agonistic contests took place in the same experimental tank. Holding and experimental tanks contained water collected and sieved from the same sites at which the crayfish were collected. All crayfish were housed in the laboratory at the natural ambient photoperiod. The same crayfish pairs used in the agonistic contests were later used in the feeding contests. Individuals from these pairs were not used in any other agonistic or feeding contest. The agonistic contest This study followed procedures established by Guiasu and Dunham (1997b). Contests were performed between 0800 and 1500 hours. Prior to initiating the contests, trials were performed to determine if there was a difference between diurnal and nocturnal trials. No differences were noted for interactions observed during these time periods (P > 0.05); however, previous studies have suggested an increase in activity and frequency of agonistic interactions during nocturnal periods in other species of crayfish (Fero et al. 2007, Issa et al. 1999). Before being placed in the experimental aquarium, a red or yellow marking was randomly placed on the cephalothorax of each opponent to easily distinguish the two crayfish. Before each agonistic contest, two crayfish of the intraspecific matched pair were placed on opposite sides of the divider and allowed to acclimate for 20 minutes. The divider was removed, and individual interactions between the two crayfish were recorded for 30 minutes using a Panasonic Digital Video Camcorder (PV-GS19). Crayfish were not disturbed during the recording period. Three types of initiation behaviors were quantified: lunge, claw raise, and ambivalent contact. The crayfish starting each agonistic interaction, the initiation behavior performed, and the outcome of the individual interactions were also recorded for each contest. The crayfish that retreated, tail-flipped, ran, or used other avoidance mechanisms was considered the loser of the individual agonistic contest, and the opponent was declared the winner. The duration of each interaction was recorded from the time that the two crayfish came in physical contact with one another until one crayfish either backed away, walked away, or tail flipped away from its opponent. The 30-minute observation period was divided into 6 2010 P.M. Stewart, A.D. McKenzie, T.P. Simon, and A.M. Baker 235 five-minute time intervals to see if the mean duration of each agonistic interaction and the number of individual interactions changed as time progressed. The feeding contest Crayfish pairs, tested previously in the agonistic contest, were isolated for one week, using the same isolation method as in the agonistic contest. To reduce the effects of feeding on motivation, crayfish were not fed for 72 hours prior to the feeding contest. Practice trials, performed in this current study, revealed that a 72-hour waiting period was the minimum time needed to practically ensure that individuals of this species of crayfish would show interest in feeding. Before each feeding contest, the intraspecific pairs were placed on opposing sides of the dividers and were allowed to acclimate for 20 minutes. The divider was removed and a night crawler, attached to a string and weight, was placed in the middle of the tank. Crayfish were recorded until a definitive winner of the food contest was established. The definitive winner of the feeding contest was the individual that successfully obtained the food item. If both subjects obtained a portion of the food item, the crayfish that obtained 60% of the food item, based on visual observations, was declared the winner. If neither obtained a larger portion, then the contest was recorded as a tie. Statistical tests All statistical analysis for the agonistic contests followed those performed in previous studies of this type (Guiasu and Dunham 1997b) using SPSS® 11.0.1. Overall winners of the agonistic interaction were determined using the percentage of overall individual wins. Due to the low sample number (n < 20), nonparametric tests were used. The Mann-Whitney U test for two independent samples (α = 0.05) was used to compare differences between the winners and losers depending on the type of initiation behavior used. A Mann-Whitney U test was also used to determine if the crayfish that initiated the first interaction would also be declared the overall winner during the 30-minute recording period and to compare size-matched pairs regarding size measurements (P = 0.05). The winners of the feeding contest were compared, using a Mann-Whitney U test, to the winners of the same pairs of crayfish in the agonistic interactions to see if the winner of the agonistic interaction also won the feeding contests. The Kruskal-Wallis H test was used to compare the number of interactions during the 6 time intervals of the 30-minute observation period (P = 0.05). Results Number of interactions observed Eight hundred and forty-one individual interactions among the 16 form I vs. form I, 20 form II vs. form II, and 13 form I vs. form II male pairs were observed during a total of 24.5 hours (1470 min) of observation. Three hundred and thirty-seven agonistic interactions occurred between form I vs. form I males, constituting 40% of the individual interactions observed 236 Southeastern Naturalist Vol. 9, Special Issue 3 among the 3 form categories, 281 interactions (33% of the total interactions) were observed between form II vs. form II males, and 223 interactions (27% of the total interactions) were observed between form I vs. form II males. Results of the agonistic contests were based on all of the individual interactions that occurred during the 30-minute recording periods. There was a significant difference among the time intervals for the form I vs. form I contests (Kruskal-Wallis H: P = 0.01), with the most interactions occurring in the second time interval and the least occurring during the fifth and sixth intervals (Fig. 1). There were, however, no significant differences found among the 6 time intervals for the form II vs. form II and form I vs. form II contests (Kruskal-Wallis H: P = 0.15 and 0.13, respectively). Mean duration of agonistic interactions There was a significant difference in the duration of interactions among the 6 time intervals for all 3 form categories (Kruskal-Wallis H: P = 0.001, for all types; Fig. 2). During form I vs. form I and form I vs. form II competitions, Figure 1. Box-andwhisker plot representing the total number of interactions observed for form I vs. form I agonistic contests during each of the six time intervals of the 30-minute recording periods. Circle indicates a possible outlier. Figure 2. Mean (± S.E.) duration of each individual interaction (recorded in seconds) observed for form I vs. form I, form II vs. form II, and form I vs. form II agonistic contests during each of the six time intervals of the 30-minute recording periods. 2010 P.M. Stewart, A.D. McKenzie, T.P. Simon, and A.M. Baker 237 there was an increase in the duration during the second interval, but an overall decrease thereafter. For form I vs. form I contests, longer interactions occurred during the first time interval than the fifth and sixth intervals, with a decline after 21 minutes. A gradual decline in the duration of each interaction was observed over time for Form II vs. Form II contests, especially during the fourth, fifth, and sixth intervals. In form I vs. form II contests, agonistic interactions during the first time interval lasted longer than those of the last interval, with a prolonged decline beginning after 26 minutes. Winner and loser initiation behavior comparisons Overall winners of form I vs. form I, form II vs. form II, and form I vs. form II contests initiated 68%, 52%, and 61% of all individual interactions, respectively. Overall winners of both form I vs. form I and form I vs. form II contests did not significantly initiate more interactions than losers (Mann- Whitney U: P = 0.25 and 0.39, respectively). However, the overall winners of form II vs. form II contests initiated significantly more interactions than losers (Mann-Whitney U: P = 0.002). Winner and loser use of each of the 3 types of initiation behaviors (ambivalent contact, claw raise, and lunge) were analyzed for the 3 form categories. During form I vs. form I contests, there were no significant differences found for the 3 types of behaviors displayed by the winners (Kruskal-Wallis H: P = 0.07). Losers, however, used significantly more claw-raise behaviors (Mann- Whitney U: P = 0.01) than either lunge or ambivalent-contact behaviors (Mann-Whitney U: P = 0.05, for both types). Winners of form II vs. form II contests, initiated significantly more interactions with claw raise behaviors than ambivalent contact behaviors (Mann-Whitney U: P = 0.005), but no significant differences were found between the claw-raise and lunge initiation behaviors or the ambivalent-contact and lunge initiation behaviors (Mann- Whitney U: P = 0.17 and 0.54, respectively). No significant differences were found among all 3 types of behaviors for the losers of the form II vs. form II contests (Kruskal-Wallis H: P = 0.433). Form I vs. form II contests were similar to form I vs. form I contests in that there were no significant differences found for the 3 types of behaviors used by the winners (Kruskal-Wallis H: P = 0.35). Losers, however, used significantly more claw-raise behaviors than either lunge (Mann-Whitney U: P = 0.01) or ambivalent-contact behaviors (Mann Whitney U: P = 0.005). Within each form category, the dominant initiation behavior used by winners was compared to the dominant behavior used by losers. During form I vs. form I contests, winners used claw-raise initiation behaviors significantly less than losers (Mann-Whitney U: P = 0.05). Form II vs. form II winners did not use lunge or claw-raise initiation behaviors significantly more than losers (Mann-Whitney U: P = 0.22 and 0.16, respectively), and winners did not use ambivalent-contact behaviors less than losers (Mann-Whitney U: P = 0.22). Results were similar for form I vs. form II contests—winners did not use more lunge or claw-raise behaviors than losers (Mann-Whitney U: P = 0.08 and 0.42, respectively), and winners did not use ambivalent-contact behaviors less than losers (Mann-Whitney U: P = 0.41). 238 Southeastern Naturalist Vol. 9, Special Issue 3 The winner of each overall contest was compared with the crayfish that initiated the first interaction to see if the crayfish that initiated the interaction would also win a majority of the total interactions. The crayfish that initiated the first interaction won 71% of the individual interactions during form I vs. form I contests, 68% during form II vs. form II contests, and 62% of the form I vs. form II contests. There were no significant differences found between the winners and losers that won the first agonistic interaction and the eventual status for all 3 form categories (Mann-Whitney U: P = 0.32, for all 3 categories). After pooling the data to observe if the crayfish initiating the first interaction was the overall winner of the contest and to increase the degrees of freedom in the statistical analysis, overall winners were found to initiate more of the first interactions than did the overall losers (Mann- Whitney U: P = 0.03). Comparison between form I and form II males Interactions between form I vs. form II males were observed to document possible hierarchical formations and agonistic behaviors between these size-matched pairs. Although, there were no significant differences found between the number of individual agonistic interactions won by form I or form II males (Mann-Whitney U: P = 0.34), the most commonly used initiation behavior by form I males was the claw raise. Form I males used the claw-raise behavior significantly more than either the lunge or the ambivalent contact behavior (Mann-Whitney U: P = 0.003 and 0.005, respectively; Fig. 3A). There were no significant differences found among the 3 initiation behaviors for form II males (Kruskal-Wallis H: P = 0.713; Fig. 3B). When comparing the behaviors of the 2 reproductive types, form I males used the claw-raise behavior to initiate more interactions than did Form II males (Mann-Whitney U: P = 0.021). There were no significant differences in use of either lunge behavior or ambivalent-contact behavior between the 2 reproductive types (Mann-Whitney U: P = 0.698 and 0.327, respectively). Agonistic and feeding contests comparison Crayfish pairs, from each form category, competed in both agonistic and feeding contests to see if the winners of the agonistic contest would also win the feeding contest. Two pairs were deleted from this analysis because either one or both of the crayfish of the agonistic pair died prior to the feeding contest or there were no interactions observed between the crayfish pair. Winners of the agonistic interactions won significantly more of the corresponding feeding contests than did the losers of form I vs. form I, form II vs. form II, and form I vs. form II contests (Mann-Whitney U: P = 0.027, 0.029, and 0.017, respectively). Discussion Differences in behavior, the number and duration of contests, and outcomes of agonistic and feeding contests were observed among the 3 form categories and between winners and losers. There was a significant decrease 2010 P.M. Stewart, A.D. McKenzie, T.P. Simon, and A.M. Baker 239 in the number of form I vs. form I contest interactions after 21 minutes, which suggests the development of hierarchical relationships among P. suttkusi form I individuals. There were no significant differences among the number of interactions that occurred during different time intervals for form II vs. form II and form I vs. form II contests, suggesting that hierarchical relationships did not form among individuals of these groups during the 30-minute observation periods. Some of the results observed for P. suttkusi in our study differed from the results found for other studies of this type. During form I vs. form I Cambarus robustus Girard (Big Water Crayfish) contests, the number of interactions began to decline in the 21- to 30-minute time interval, which is similar to results of this study (Guiasu and Dunham 1997b). However, a gradual decline in the number of interactions were observed over time for form I vs. form I C. robustus (Guiasu and Dunham 1997b), while observations of form II vs. form II contests for C. robustus suggested a decline in the number of interactions only in the last 30 minutes of the observation period (Guiasu and Dunham 1997a). During form I vs. form II contests, the number of interactions was significantly greater in the second time interval Figure 3. Box-and-whisker plots representing the total number of initiation behaviors displayed by A) form I and B) form II males during form I vs. form II agonistic contests. 240 Southeastern Naturalist Vol. 9, Special Issue 3 than the last, with a decline suggested after 51 minutes (Guiasu and Dunham 1998). The recording period for our study may have not been long enough to reveal a significant decline in the number of interactions for form II vs. form II and form I vs. form II contests. Because some decline was suggested, and the form I vs. form I individual interactions declined at the same time interval for studies of this type by Guiasu and Dunham (1997a), it is likely that a 60-minute recording period would have revealed a significant decline for these paired interactions as time progressed. The decline in agonistic interactions may be linked to the establishment of the dominant-subordinate relationship between the two interacting individuals. In the present study, a significant decrease in the mean duration of each interaction was observed for all 3 form categories. Declines were observed after 11 minutes for form I vs. form I, 16 minutes for form II vs. form II, and 21 minutes for form I vs. form II contests. Our results were similar to those provided by other studies for C. robustus, in which there was a decline found at 21 minutes for form I vs. form I contests (Guiasu and Dunham 1997a), 31 minutes for form II vs. form II contests (Guiasu and Dunham 1997b), and 51 minutes for form I vs. form II contests (Guiasu and Dunham 1998). There were distinguishable differences observed among the Guiasu and Dunham studies (1997a, 1997b, 1998), possibly suggesting that the point at which interactions begin to decline is species and form specific. Regardless of exactly when the period of time engaged in agonistic interactions declined, there appears to be a clear decrease in the duration of these interactions over time. Other studies, using different species, have documented winners using more lunge and claw-raise behaviors than ambivalent behaviors during form I vs. form I and form II vs. form II contests (Guiasu and Dunham 1997b, 1998), which supports the findings on the claw-raise behavioral preference by winners of form II vs. form II individuals of this study. However, loser preference of ambivalent contact behaviors in other studies (Guiasu and Dunham 1997b, 1998) did not support loser preference of claw-raise behavior in this study, suggesting that this behavior in form I vs. form I contests may be species specific in P. suttkusi males. For form I vs. form II contests (Guiasu and Dunham 1997a), winners used the claw-raise behavior more than any other type, but there were no significant differences among the behaviors of the losers. During form I vs. form I and form I vs. form II contests, there were no significant differences found among the initiation behaviors used by the winners, but the losers preferred to use the claw-raise initiation behavior more than any other initiation behavior. Winners of form II vs. form II contests in the current study used claw-raise initiation behaviors more than any other type of behavior, but they did not significantly perform more claw-raise behaviors than the losers of these interactions. Because the winners and losers in the current study did not prefer the same initiation behaviors as other studies, the types of initiation behaviors demonstrated by crayfish may be species specific. Tierney et al. (2000) compared the intraspecific agonistic behaviors of 4 crayfish species and found that each species preferred to use certain initiation behaviors more 2010 P.M. Stewart, A.D. McKenzie, T.P. Simon, and A.M. Baker 241 than others. There were also different use patterns observed among the 3 form categories in the current study and other behavioral studies suggesting that winner and loser preferences for lunge, claw-raise, and ambivalent-contact behaviors may also be form specific. Form I males did not win significantly more contests than form II males in the present study; however, during form I vs. form II C. robustus male contests, form I males won significantly more agonistic contests than form II males (Guiasu and Dunham 1998). Guiasu and Dunham (1998) found that form I C. robustus males used the claw-raise behavior more than any other initiation behavior. Similar results were observed for the current study, form I P. suttkusi males used the claw-raise behavior more than any other type of initiation behavior, but no preference was found for form II males in this species. In this study, crayfish were size-matched with no significant difference found among all measurements, which may have caused results to be different from the studies by Guiasu and Dunham (1998). Guiasu and Dunham (1998) found winners to be significantly larger than losers in all measurements, except for cephalothorax length. In addition, differences in observational periods between the two studies may also have caused these differences because Guiasu and Dunham (1998) observed interactions for 60 minutes, while interactions were only observed for 30 minutes in the present study. In the present study, form I males did not dominate form II males; however, this study only documented size-matched form I vs. form II P. suttkusi pairs. Further research using pairs that are not size-matched may be needed to better understand agonistic interactions between the two male reproductive forms of this species. Guiasu and Dunham (1997a, 1997b, and 1998) compared form differences compounded by size differences for several variables. Any study examining size differences must use the same form, and conversely, any study comparing form differences must use size-matched pairs as in the present study. Winners of the agonistic contests also won significantly more of the feeding contests than losers. Dominance has often been linked to the ability of crustaceans to obtain valuable resources (Goessmann et al. 2000). Orconectes rusticus, an invasive species, dominated native Orconectes sp., in both agonistic contests and shelter trials (Klocker and Strayer 2004). Another study of O. rusticus revealed that this species competed for food using aggressive interactions, and that these interactions escalated as these resources became limited (Capelli and Hamilton 1984). Procambarus clarkii (Girard) (Red Swamp Crawfish) was able to aggressively dominate a sympatric species, P. zonangulus Hobbs and Hobbs (Southern White River Crawfish), in shelter competitions, indicating an aggressive advantage for P. clarkii (Blank and Figler 1996). However, some studies suggest that, while dominant status influences behavioral decisions, it has less of an impact on feeding and mating success in crayfish (Fero et al. 2007). Results of the above-mentioned studies and the present one disagree with Fero et al. and provide further evidence that winners of agonistic interactions may dominate valuable resources. 242 Southeastern Naturalist Vol. 9, Special Issue 3 Because some of the results on initiation behaviors and behavioral preference between winners and losers and among form categories in this study disagree with findings of previous studies, behavioral dynamics in P. suttkusi males may be species specific. Although reproductive form in P. suttkusi males was not found to significantly influence dominance, winners of agonistic contests were more likely to win feeding contests. When the data was pooled, this study suggested that P. suttkusi individuals initiating agonistic interactions are more likely to become dominant in size-matched contests regardless of reproductive form. Thus, aggressive P. suttkusi males might gain improved access to food resources. In this species, when size-matched pairs were examined, dominance may be related to the internal motivational state of the organism and not related to form. A more aggressively motivated individual, regardless of the form, also tended to win the feeding competition. Aggressiveness may be limited by survivability, as overly aggressive individuals may be subject to increased predatory losses. Acknowledgments The authors thank Dr. Stephen Landers and Dr. Allen Tubbs for editorial assistance. Thanks to Raymond McCall, Troy Baker, and Robert Yoder for field assistance, and to Stuart Welsh for publication support. This project was supported by the ALFA Fellowship at Troy University. The publication of this manuscript was supported, in part, by the US Geological Survey Cooperative Research Unit Program, including the West Virginia Cooperative Fish and Wildlife Research Unit. Literature Cited Baird, H.P., B.W. Patullo, and D.L. Macmillan. 2006. Reducing aggression between freshwater crayfish (Cherax destructor Clark: Decapoda, Parastacidae) by increasing habitat complexity. Aquaculture Research 37:1419–1428. Baker, A.M., P.M. Stewart, and T.P. Simon. 2008. Life-history study of Procambarus suttkusi in southeastern Alabama. Journal of Crustacean Biology 28:451–460. Barki, A., I. Karplus, and M. Goren. 1992. Effects of size and morphotype on dominance hierarchies and resource competition in the freshwater prawn Macrobrachium rosenbergii. Animal Behaviour 44:547–555. Bergman, D.A., and P.A. Moore. 2003. Field observations of intraspecific agonistic behavior of two crayfish species, Orconectes rusticus and Orconectes virilis, in different habitats. Biological Bulletin 205:26–35. Bergman, D.A., C.P. Kozlowski, J.C. McIntyre, R. Huber, A.G. Daws, and P.A. Moore. 2003. Temporal dynamics and communication of winner-effects in the crayfish, Orconectes rusticus. Behaviour 140:805–825. Blank, G.S., and M.H. Figler. 1996. Interspecific shelter competition between the sympatric crayfish species Procambarus clarkii (Girard) and Procambarus zonangulus (Hobbs and Hobbs). Journal of Crustacean Biology 16:300–309. Bouchard, R.W. 1976. Crayfishes and shrimps. Bulletin of the Alabama Museum of Natural History 2:13–20. Capelli, G.M., and P.A. Hamilton. 1984. Effects of food and shelter on aggressive activity in the crayfish Orconectes rusticus (Girard). Journal of Crustacean Biology 4:252–260. 2010 P.M. Stewart, A.D. McKenzie, T.P. Simon, and A.M. Baker 243 Copp, N.H. 1986. Dominance hierarchies in the crayfish Procambarus clarkii (Girard, 1852) and the question of learned individual recognition (Decapoda, Astacidea). Crustaceana 51:9–24. Edsman, L., and A. Jonsson. 1996. The effect of size, antennal injury, ownership, and ownership duration on fighting success in male signal crayfish, Pacifastacus leniusculus (Dana). Nordic Journal of Freshwater Research 72:80–87. Evans, D.L., and M. Shehadi-Moacdieh. 1988. Body size and prior residency in staged encounters between female prawns, Palaemon elegans Rathke (Decapoda: Palaemonidae). Animal Behaviour 36:452–455. Fero, K., J.L. Simon, V. Jourdie, and P.A. Moore. 2007. Consequences of social dominance on crayfish resource use. Behaviour 144:61–82. Figler, M.H., H.M. Cheverton, and G.S. Blank. 1999. Shelter competition in juvenile Red Swamp Crayfish (Procambarus clarkii): The influences of sex differences, relative size, and prior residence. Aquaculture 178:63–75. Fitzpatrick, J.F., Jr. 1990. Decapoda. Preliminary consideration of endangered invertebrates in Alabama. Journal of the Alabama Academy of Science 61:64–92. Gherardi, F., and W.H. Daniels. 2003. Dominance hierarchies and status recognition in the crayfish Procambarus acutus acutus. Canadian Journal of Zoology 81:1269–1281. Gherardi, F., P. Acquistapace, and S. Barbaresi. 2000. The significance of chelae in the agonistic behaviour of the White-clawed Crayfish, Austropotamobius pallipes. Marine and Freshwater Behaviour and Physiology 33:187–200. Goessmann, C., C. Hemelrijk, and R. Huber. 2000. The formation and maintenance of crayfish hierarchies: Behavioral and self-structuring properties. Behavioral Ecology and Sociobiology 48:418–428. Guiasu, R.C., and D.W. Dunham. 1997a. Agonistic interactions in male form II Cambarus robustus Girard, 1852 crayfish (Decapoda, Cambaridae) and a comparison between male form I and form II intra-form contests. Crustaceana 70:720–736. Guiasu, R.C., and D.W. Dunham. 1997b. Initiation and outcome of agonistic contests in male form I Cambarus robustus Girard, 1852 crayfish (Decapoda, Cambaridae). Crustaceana 70:480–496. Guiasu, R.C., and D.W. Dunham. 1998. Inter-form agonistic contests in male crayfishes, Cambarus robustus (Decapoda, Cambaridae). Invertebrate Biology 117:144–154. Guiasu, R.C., and D.W. Dunham. 1999. Aggressive interactions between the crayfishes Cambarus bartonii bartonii and C. robustus (Decapoda: Cambaridae): Interspecific and intraspecific contests. Journal of Crustacean Biology 19:131–146. Hazlett, B.A. 1997. The organisation of behaviour in hermit crabs: Responses to variation in stimulus strength. Behaviour 134:59–70. Hazlett, B.A., F.E. Anderson, L.A. Esman, C. Stafford, and E. Munro. 1992. Interspecific behavioral ecology of the crayfish Orconectes rusticus. Journal of Freshwater Ecology 7:69–76. Heath, W.H., P. M. Stewart, T.P. Simon, and J.M. Miller. 2010. Distributional survey of crayfish (Crustacea: Decapoda) in wadeable streams in the coastal plains of southeastern Alabama. Southeastern Naturalist 9(Special Issue 3):139–154. Herberholz, J., M.M. Sen, and D.H. Edwards. 2003. Parallel changes in agonistic and non-agonistic behaviors during dominance hierarchy formation in crayfish. Journal of Comparative Physiology A 189:321–325. 244 Southeastern Naturalist Vol. 9, Special Issue 3 Hobbs, H.H., Jr. 1953. A new crayfish of the genus Procambarus from Alabama and Florida (Decapoda, Astacidae). Proceedings of the Biological Society of Washington 66:173–178. Hobbs, H.H., Jr. 1981. Crayfishes of Georgia. Smithsonian Contributions to Zoology 318:1–549. Issa, F.A., D.J. Adamson, and D.H. Edwards. 1999. Dominance hierarchy formation in juvenile crayfish Procambarus clarkii. Journal of Experimental Biology 202:3497–3506. Karavanich, C., and J. Atema. 1998. Individual recognition and memory in lobster dominance. Animal Behaviour 56:1553–1560. Karnofsky, E.B., J. Atema, and R.H. Elgin. 1989. Field observations of social behavior, shelter use, and foraging in the Lobster, Homarus americanus. Biological Bulletin 176:239–246. Klocker, C.A., and D.L. Strayer. 2004. Interactions among an invasive crayfish (Orconectes rusticus), a native crayfish (Orconectes limosus), and native bivalves (Sphaeriidae and Unionidae). Northeastern Naturalist 11:167–178. Krebs, J.R., and N.B. Davies. 1987. An Introduction to Behavioral Ecology. Blackwell Scientific Publications, Boston, MA. 389 pp. Lowe, M.E. 1956. Dominance-subordinance relationships in the crawfish Cambarellus shufeldtii. Tulane Studies in Zoology 4:139–170. Lundberg, U. 2004. Behavioural elements of the Noble Crayfish, Astacus astacus (Linnaeus, 1758). Crustaceana 77:137–162. May, H.Y., and A.J. Mercier. 2006. Responses of crayfish to a reflective environment depend on dominance status. Canadian Journal of Zoology 84:1104–1111. Nakata, K., and S. Goshima. 2003. Competition for shelter of preferred sizes between the native crayfish species Cambaroides japonicus and the alien crayfish species Pacifastacus leniusculus in Japan in relation to prior residence, sex difference, and body size. Journal of Crustacean Biology 23:897–907. Quinn, J.P., and J. Janssen. 1989. Crayfish competition in southwestern Lake Michigan: A predator-mediated bottleneck. Journal of Freshwater Ecology 5:75–85. Rorer, W.E., and G.M. Capelli. 1978. Competition interaction between two Mountain Lake crayfish species with life-history notes. Virginia Journal of Science 29:245–248. Rubenstein, D.I., and B.A. Hazlett. 1974. Examination of the agonistic behaviour of the crayfish Orconectes virilis by character analysis. Behaviour 50:193–216. Schroeder, L., and R. Huber. 2001. Fight strategies differ with size and allometric growth of claws in crayfish, Orconectes rusticus. Behaviour 138:1437–1449. Smith, M.R., and D.W. Dunham. 1990. Chela posture and vision: Compensation for sensory deficit in the crayfish Orconectes propinquus (Girard) (Decapoda, Cambaridae). Crustaceana 59:309–313. Snedden, W.A. 1990. Determinants of male mating success in the temperate crayfish Orconectes rusticus: Chela size and sperm competition. Behaviour 115:101–113. Söderbäck, B. 1991. Interspecific dominance relationship and aggressive interactions in the freshwater crayfishes Astacus astacus (L.) and Pacifastacus leniusculus (Dana). Canadian Journal of Zoology 69:1321–1325. Stein, R.A. 1976. Sexual dimorphism in crayfish chelae: Functional significance linked to reproductive activities. Canadian Journal of Zoology 54:220–227. Tierney, A.J., M.S. Godleski, and J.R. Massanari. 2000. Comparative analysis of agonistic behavior in four crayfish species. Journal of Crustacean Biology 20:54–66.