Radu Cornel Guiasu

Aggressive Interactions Between the Crayfishes Cambarus Bartonii Bartonii and C. Robustus (Decapoda: Cambaridae): Interspecific and Intraspecific Contests

ABSTRACT In the Province of Ontario, Canada, the two closely related crayfish species, Cambarus bartonii bartonii and Cambarus robustus, appear to have similar habitat requirements and similar, asynchronous life cycles, but largely nonoverlapping distributions. The analysis of the interspecific agonistic contests between size-matched males of these two species showed that C. robustus were clearly dominant over C. b. bartonii of similar size. At the same time, C. robustus performed significantly more Lunge and Claws Raised initiation behaviors than C. b. bartonii, during these contests. These two initiation behaviors were strongly indicative of dominant status during intraspecific contests of C. robustus. Cambarus robustus behaved more aggressively toward C. b. bartonii than toward other conspecifics. Cambarus b. bartonii performed significantly more tail-flip escape behaviors than C. robustus. Juvenile C. robustus were dominant over adult C. b. bartonii in a majority of these contests. The clear dominance of C. robustus over C. b. bartonii during agonistic contests, and the apparent recent expansion of the range of C. robustus in Ontario, sometimes at the expense of C. b. bartonii, suggest that C. robustus has the potential to competitively exclude C. b. bartonii, if the two species are in competition for limited resources such as shelters.

INTER-FORM AGONISTIC CONTESTS IN MALE CRAYFISHES, CAMBARUS ROBUSTUS (DECAPODA, CAMBARIDAE)

In this study, we evaluate the aggressive interactions between breeding form (Form I) and non-breeding form (Form II) male crayfishes, Cambarus robustus, during inter-form contests, and compare these data to those from previous studies on intra-form contests in this species. The analysis of inter-form agonistic contests between size-matched crayfishes showed that Form I males were clearly dominant, in most cases, over Form II males. Furthermore, Form I males performed significantly more Lunge and Claws Raised initiation behaviors than Form II males during these contests. These two initiation behaviors strongly indicate the dominant status of individuals in both inter-form and intra-form contests. Form I winners performed significantly more aggressive Claws Raised initiation acts in the inter-form contests, against Form II conspecifics, than in intra-form contests against other Form I conspecifics. Male form is an important variable in the agonistic interactions of cambarid crayfishes. In C. robustus, adult males of both forms coexist in the same populations throughout the year. Thus, Form I and Form II males may compete with one another for access to potentially limiting resources. Additional key words: dominant, subordinate, initiation behaviors Cambarus robustus GIRARD 1852 (Decapoda, Cambaridae) is a large crayfish species whose distribution within Canada, at the northern edge of its range, is restricted to fast-flowing streams and some Precambrian Shield lakes located in southern and south-central Ontario (Guiasu et al. 1996a). In the United States, this species is found primarily in the Ohio River and Great Lakes (except for Lake Superior) drainage basins (Crocker & Barr 1968). Adult male crayfishes of the family Cambaridae exhibit sexual dimorphism (Fig. 1) characterized by cyclical alternation between a breeding form (Form I) and a non-breeding form (Form II) (Hobbs 1991). This sexual dimorphism and the corresponding cyclical alternation between male forms are unique among decapod crustaceans (Hobbs 1974, 1988). In at least one cambarid crayfish species, Procambarus spiculifer, the alternation between Form I and Form II appears to be absent, and Form II males seem to represent a developmentally intermediate stage between the juvenile and Form I stages (Taylor 1985). The complete cyclical alternation between the two male forms is, however, present in other cambarid crayfish species (Hobbs a Author for correspondence. E-mail: radu@zoo.toronto.edu 1974), including C. robustus (Hamr & Berrill 1985; Guiasu, unpubl. data). In Form I males, the distal elements of the copulatory stylets (highly specialized first male pleopods) are more heavily sclerotized and better differentiated (Fig. 2), the ischial hooks on one or more of the second to fourth pereiopods are more prominent, and the major chelae (claws) are larger, relative to the cephalothorax length, than in Form II males (Crocker & Barr 1968, Stein 1976, Hobbs 1991). Word & Hobbs (1958) showed that the sperm ducts of Form I males contained many recently formed spermatids. Such dimorphism in male morphology is often strongly influenced by sexual selection (Andersson 1994). Stein (1976) showed that, in the crayfish species Orconectes propinquus, males with relatively larger chelae were more successful in copulating with females and in the aggressive interactions with other males for access to females, compared to males with smaller chelae. Males with relatively larger chelae should also have an advantage over crayfishes with smaller chelae in the competition for potentially limiting resources such as

DISTRIBUTION AND STATUS OF CRAYFISHES OF THE GENERA CAMBARUS AND FALLICAMBARUS (DECAPODA: CAMBARIDAE) IN ONTARIO, CANADA

ABSTRACT This comprehensive update of the distribution of crayfishes of the genera Cambarus and Fallicambarus in Ontario includes substantial material collected since 1965 and a reexamination of previous records. Revised provincial range limits are presented for two wide-ranging, openwater species, C. bartonii bartonii and C. robustus, as well as for 2 obligate burrowers of more restricted distribution, C. diogenes and F. fodiens. Previously unreported locality records represent range extensions, fill in geographic gaps in known ranges, or confirm the persistence of populations for periods of several decades. Limits to the ranges of the 4 species appear to be established by patterns of postglacial migration and habitat preferences. A diagnosis of the current status of each of these species suggests the potential impact of anthropogenic perturbations, such as lake acidification and wetland destruction, for the future of these crayfishes in Ontario.

Conditional and weighted measures of ecological diversity

Shannons entropy and Simpsons index are the most used measures of species diversity. As the Simpson index proves to be just an approximation of the Shannon entropy, conditional Simpson indices of diversity and a global measure of interdependence among species are introduced, similar to those used in the corresponding entropic formalism from information theory. Also, since both the Shannon entropy and the Simpson index depend only on the number and relative abundance of the respective species in a given ecosystem, the paper generalizes these indices of diversity to the case when a numerical weight is attached to each species. Such a weight could reflect supplementary information about the absolute abundance, the economic significance, or the conservation value of the species.

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

An analysis of intra-form agonistic contests between size-matched male Form II (non-breeding form) Cambarus robustus Girard, 1852 crayfish revealed that the winners and losers of these contests differed in the numbers and types of initiation behaviours used. The (eventual) winners, which initiated significantly more fights overall, used mostly the aggressive Claws Raised and Lunge initiation behaviours, whereas the (eventual) losers, which also initiated most of the very first fights of the overall agonistic contests, used mostly the tentative Ambivalent Contact behaviour. Thus, initiation behaviours can be used as good predictors of status for males of this species. The Lunge behaviour is a strong indicator of the eventual dominant status of male crayfish, during agonistic contests. There was a significant, negative correlation between the relative frequency of the Lunge initiation behaviours used by the winners and the total time spent fighting. A comparison between the male Form II and Form I (breeding form) intra-form contests, in this species, and an analysis of the differences and similarities between these two types of contests, indicated that male form is an important variable in the agonistic interactions of cambarid crayfish.

NEW MEASURES FOR COMPARING THE SPECIES DIVERSITY FOUND IN TWO OR MORE HABITATS

Both the weighted entropy, which generalizes the Shannon entropy, and the weighted quadratic index, which generalizes the Gini-Simpson index, are used for getting a unified treatment of some diversity measures proposed recently in ecology. The weights may reflect the ecological importance, rarity, or economic value of the species from a given habitat. The weighted measures, being concave functions, may be used in the additive partition of diversity. The weighted quadratic index has a special advantage over the weighted entropy because its maximum value has a simple analytical formula which allows us to introduce a normed measure of dissimilarity between habitats. A special case of weighted quadratic index is the Rich-Gini-Simpson index which, unlike the Shannon entropy and the classic Gini-Simpson index, behaves well when the number of species is very large. The weighted entropy and the weighted quadratic index may also be used to measure the global diversity among the subsets of species. In this context, Raos quadratic index of diversity between the pairs of species, based on the phylogenetic distance between species, is obtained as a particular case and is generalized to measure the diversity among the triads of species as well.