Francesca Gherardi

Previous studies have shown that the American lobster, Homarus americanus, is able to recognize the identity of conspecifics. To be recognized, a lobster should bear unique phenotypic traits that are unlikely to be confused in the population. Our aim here was to investigate, in H. americanus, some variable phenotypes that could be good candidates for ‘identity signatures’. Five colour parameters of 44 spots distributed on the body of 12 adult males were measured. We also measured 10 features of the face in 13 adult male lobsters, and 7 and 5 features of the crusher and the cutter chelae, respectively, in 8 of these individuals. Principal Component Analyses showed a clear interindividual difference in colour patterns and a large variation of facial and chelar morphology. The most variable features were: the shape of the face plus the size and distance between the eyes and the orbital spines; the number, size and shape of the molar-like teeth of the crusher chelae plus the number of its spines; and the size of the dactyl of the cutter chelae plus the number of its incisor-like teeth and spines. Obviously, before concluding that colour and morphological features are identity signatures in H. americanus, behavioural studies and an increased knowledge of visual acuity and colour sensitivity in this species are needed. Nevertheless, the similarity of our results with findings on the crayfish Cherax destructor is intriguing and stimulates further research.

Despite their key role as model organisms in many behavioral studies, crustacean decapods have been only slightly touched upon by the recent surge of scientific interest in animal personality. Only seven articles investigated the issue in a handful of species among hermit crabs, crabs, and crayfish. Obviously, a limited number of publications does not mean that personality is rare in decapods. On the contrary, few studies might be the result of a form of reluctance by behavioral ecologists to deal with such a phenomenon in these and other invertebrates. This reluctance contrasts with the enthusiasm shown in tackling the behavioral plasticity issue. Here we discuss the possible theoretical and methodological difficulties raised by applying the animal personality perspective to decapods and analyze implications of personality studies for their ecology, conservation, and welfare. By highlighting gaps in knowledge and directions of future research, our intention is to increase scientific emphasis on the issue.

Since the 1970s, the ability of some invertebrate species to recognize individual conspecifics has attracted increased scientific interest. However, there is still confusion in the literature, possibly due to the lack of unambiguous criteria for classifying social recognition in its different forms. Here, we synthesize the results of studies on invertebrates and provide a framework with the purpose of identifying research needs and directions for future investigations. Following in part Sherman et al.’s (Behavioural ecology: an evolutionary approach. Blackwell Science, Oxford, pp 69–96, 1997) definition of ‘recognition systems’ and Tibbetts and Dale’s (Trends Ecol Evol 22:529–537, 2007) classification of ‘individual recognition,’ we first discuss different case studies that exemplify the categories of ‘familiar recognition’ and ‘class-level recognition.’ Then, through the analysis of the invertebrate literature, we illustrate eight key properties that characterize ‘true individual recognition’ systems. We are confident that the proposed framework will provide opportunities for exciting discoveries of the cognitive abilities in invertebrates.

Whether invertebrates are able or not to experience pain is a highly controversial issue. An operative way to solve such a controversy might be to investigate their responses to potentially noxious stimuli and to collect evidence of their behavioural complexities as proxies of cognitive capacities. The principle of argument-by-analogy can be then applied to these data: the behaviour displayed by invertebrates is compared with that of "higher" animals, its similarity denoting the former's capacity to have analogous experiences. Here, the author discusses some examples, extracted from the literature on crustacean decapods, that pinpoint their nature of "sentient" animals. This review, however, also shows that research is still scanty in the field. The studies that examine the potential links between stress responses and pain experience are few, and the several papers that help elucidate cognitive abilities in decapods have been limited to a few taxa and are not specifically directed to the question of "sentience". On the contrary, also in the light of the expected revision of the current EU legislation in the matter, more scientific efforts should be expended on exploring the issue of pain experience in invertebrates.

Genetic studies have shown that the threatened crayfish Austropotamobius pallipes species complex is composed of two lineages (A. italicus and A. pallipes), both occurring in Italy. However, the issue surrounding their taxonomic status has not yet been solved even though the confused taxonomy may hamper attempts to conserve indigenous crayfish. The aim of this study was to develop methods for the morphometrical characterization of the A. pallipes species complex. Having analysed 18 morphometric variables on a total of 44 specimens of each lineage, we showed that the tip of the rostrum could be used to discriminate A. italicus and A. pallipes. Such discrimination was also obtained by analysing the size and shape of both the female spermatophoric plate and the male gonopods. These results confirm the potential to adopt morphometric studies to complement the genetic characterization of cryptic species.