Delayed courtship in the fiddler crab Uca musica terpsichores

Exoskeletal Trade-off between Claws and Carapace in Deep-sea Hydrothermal Vent Decapod Crustaceans

Limitations on energetic resources create evolutionary trade-offs, prompting us to investigate if investment in claw strength remains consistent across crustaceans living in diverse habitats. Decapod crustaceans living in deep-sea hydrothermal vents are ideal for this study due to their extreme environment. In this study, we investigated whether decapods (blind crab Austinograea sp. and the squat lobster Munidopsis lauensis) living in deep-sea hydrothermal vents prioritize investing in strong claws compared to the carapace, like coastal decapods. We analyzed exoskeleton morphology, mechanical properties, structures, and elemental composition in both the carapace and claws of four Decapoda species (two each from Brachyura and Anomura infraorders) in vent and coastal habitats. Coastal decapods had ∼4-9 times more teeth on their claw cutting edge than the vent species. Further, only the coastal species exhibited higher firmness in their claws than in their carapaces. Each infraorder controlled exoskeletal hardness differently: Brachyura changed the stacking height of the Bouligand structure, while Anomura regulated magnesium content in the exoskeleton. The vent decapods may prioritize strengthening their carapace over developing robust claws, allocating resources to adapt to the harsh conditions of deep-sea hydrothermal vents. This choice might enhance their survival in the extreme environment, where carapace strength is crucial for protecting internal organs from environmental factors, rather than relying on the powerful claws seen in coastal decapods for a competitive advantage.

Does male reproductive effort increase with age? Courtship in fiddler crabs

Theory suggests that reproductive effort generally increases with age, but life-history models indicate that other outcomes are possible. Empirical data are needed to quantify variation in actual age-dependence. Data are readily attainable for females (e.g. clutch per egg size), but not for males (e.g. courtship effort). To quantify male effort one must: (i) experimentally control for potential age-dependent changes in female presence; and, crucially, (ii) distinguish between the likelihood of courtship being initiated, the display rate, and the total time invested in courting before stopping ('courtship persistence'). We provide a simple experimental protocol, suitable for many taxa, to illustrate how to obtain this information. We studied courtship waving by male fiddler crabs, Uca annulipes. Given indeterminate growth, body size is correlated with age. Larger males were more likely to wave at females and waved more persistently. They did not, however, have a higher courtship rate (waves per second). A known female preference for males with higher display rates explains why, once waving is initiated, all males display at the same rate.

An evaluation of lekking behavior in the fiddler crab Uca spp

The reproductive behavior of Uca spp. has been extensively studied, especially the relationships between the dimorphically enlarged male claw and reproductive success. In contrast, little is known about the apparent congregations of adult males in marsh areas lacking vegetative cover where they engage in behaviors thought to attract mates. Similar congregations and displays in avian and mammalian species are termed 'leks.' In order to test the hypothesis that open-area assemblages of Uca spp. are functioning as leks, we examined the sex ratios, juvenile/adult ratios, and the percentage of time that adult males spend eliciting reproductive behaviors within open and vegetated areas of marsh habitats. Moreover, to evaluate whether differences in sediment-based food resources could explain open-area aggregations, we compared substratum organic content of open and vegetated areas of marsh habitats. Substrate was also examined to determine if grain size composition varied between open and vegetated areas and might preclude the construction of breeding burrows in vegetated areas of the marsh. Three species of Uca from four marsh habitats in biogeographically distinct regions of North America were sampled including Dauphin Island, Alabama, Hunting Island, South Carolina, Saxis, Virginia, and Wallops Island, Virginia. Comparisons of male/female and juvenile/adult ratio means indicated that greater numbers of adult males occurred in open areas of all marshes. In addition, adult males allocated significantly greater time to reproductive behaviors in open rather than in vegetatively covered areas across-all biogeographic regions and among all species. Food levels (sediment organic content) in open areas were equal to or less than sediment organic contents in vegetated areas in marsh habitats at Dauphin Island and Hunting Island, the two marshes where the variable was examined. Similarly, substratum granulometry analysis revealed no significant differences between open and vegetatively covered areas of the marshes at Dauphin Island or Hunting Island that might influence choice of burrow location. Collectively, these observations support the hypothesis that lek behavior is an integral component of the reproductive repertoire in Uca spp.