No abstract

Lysmata pederseni, a protandric simultaneously hermaphroditic shrimp that inhabits the tube sponge Callyspongia vaginalis, is monogamous in the central and southeastern Caribbean Sea. We tested the null hypothesis of monogamy in a northern Caribbean population. In the Florida Keys, shrimps did not inhabit host individuals in pairs with a frequency greater than expected by chance alone. Hermaphrodites inhabited sponges solitarily and often brooded embryos. Hermaphrodites do not store sperm and need to be inseminated shortly after molting to fertilize a new batch of eggs. Thus, males and/or other hermaphrodites are likely switching among host individuals in search of sexual partners. Field experiments demonstrated low shrimp host fidelity. Host residence time was *2 times shorter for males than for hermaphrodites. We inferred a polygynandrous mating system from L. pederseni from the Florida Keys, with male-role and young hermaphrodites often moving among sponges in search of older, more sedentary, female-role hermaphrodites. We expected shrimps to use water-borne chemical cues originating from conspecifics or sponges to locate sexual partners. Experiments demonstrated that shrimps were attracted to waterborne cues originating from sponges but not conspecifics. We have described the mating system of a reef-associated shrimp in a fast-pace shifting seascape increasingly dominated by sponges and vanishing stony corals. In the central and southeastern Caribbean Sea, with greater coral cover and lower sponge abundance than in the Florida Keys, the same species is monogamous. Whether or not similar shifts in the social organization of other coral reef-dwelling marine organisms are occurring due to contemporary changes in seascapes is a relevant topic that deserves further attention.

Theory predicts that monogamy is adaptive in resource-specialist symbiotic crustaceans inhabiting relatively small and morphologically simple hosts in tropical environments where predation risk away from hosts is high. We tested this prediction in Pontonia manningi, a hyper-symbiotic shrimp that dwells in the mantle cavity of the Atlantic winged oyster Pteria colymbus that, in turn, infects gorgonians from the genus Pseudopterogorgia in the Caribbean Sea. In agreement with theory, P. manningi were found dwelling as heterosexual pairs in oysters more frequently than expected by chance alone. Males and females also inhabited the same host individual independent of the female gravid condition or of the developmental stage of brooded embryos. While the observations above argue in favor of monogamy in P. manningi, there is evidence to suggest that males of the studied species are moderately promiscuous. That females found living solitary in oysters most often brooded embryos, and that males allocated more to weaponry (major claw size) than females at any given size suggest that males might be roaming among host individuals in search of and, fighting for, receptive females. All available information depicts a rather complex mating system in P. manningi: primarily monogamous but with moderately promiscuous males.

Many crustaceans live in intimate association with larger host animals, mostly for shelter and food. Host recognition and location behaviors by these crustaceans, and other symbionts, are vital in the life history of most symbioses. The pinnotherid crab Tunicotheres moseri (Rathbun, 1918) is a common symbiont with various solitary ascidians throughout its reported range of Jamaica, Venezuela, and West Florida. Sensory cues affecting host recognition, host use, and mate acquisition in the West Florida crab population were the focus of this study. T. moseri responded to host generated and conspecific (males responded to non-gravid females) waterborne chemical cues. Although host generated waterborne chemical cues were recognized by T. moseri, access to direct contact (which could involve chemical, visual and tactile cues) with host ascidians triggered much stronger responses. Results of conditioning trials suggest that T. moseri is a generalist, but prefers Styela plicata even after conditioning with the novel host species Molgula occidentalis and Phallusia nigra. These results show that T. moseri employs the use of multiple senses in establishing symbioses with host tunicates, and the plasticity of the responses allow potentially novel tunicates to serve as hosts. Finally, this study shows that male T. moseri, which typically only enter tunicates for breeding purposes, use waterborne cues to find tunicates housing potential female mates.

Rensch's rule, a well-studied macroevolutionary pattern of sexual size dimorphism (SSD), predicts, in monophyletic taxa in which males are the larger sex, that as the body size of the species in the clade increases, SSD increases as well. We tested Rensch's rule in the superfamily Majoidea, a diverse clade of 'spider crabs.' Considering that having the widest range of data available is important when testing macroevolutionary hypotheses, we first explored SSD in the pygmy spider crab Petramithrax pygmaeus (Bell, 1836), one of the smallest spider crabs in the superfamily. Petramithrax pygmaeus exhibits an unusual pattern of sexual dimorphism, with females displaying a larger average carapace width than males, yet males attain a larger overall body size. This type of SSD is unusual for spider crabs, with most species displaying male-biased sexual size dimorphism for both mean and overall body size. Hierarchical cluster and discriminant analyses demonstrated the existence of two distinct ontogenetic phases in P. pygmaeus (juvenile/prepubertal and adult/postpubertal). We used our data on body size of P. pygmaeus along with previously published body-size data for 11 other species within the superfamily Majoidea to test for Rensch's rule. Using raw data, phylogenetic independent contrasts generated from maximum likelihood (ML) and Bayesian inference (BI) phylogenetic trees, and reduced major axis regression analyses, we determined that for the tested species in the Majoidea that the predictions of Rensch's rule were not upheld. Macroevoultionary patterns such as Rensch's rule are not well studied in marine invertebrate systems; looking at how these rules compare between vertebrate and invertebrate and terrestrial and aquatic animals will help us to understand the differences and factors that could influence size and growth in these systems.