Abstracts (first author)
Contrasting shape, color plasticity and habitat use indicate morph-specific roles in a marine shrimpPDF
Color and shape polymorphisms are important traits of species, allowing a more generalist strategy and a better use of resources. An efficient occupation of space may lead to very abundant populations, triggering density‐dependent processes and alternative mating systems. Hippolyte obliquimanus is a small gonochoristic shrimp species, and supposedly a generalist algal dweller in shallow waters. Yet, populations comprise two main morphotypes, homogeneous shrimps of variable color (H) and transparent individuals with disruptive stripes or bands (D). H color patterns tend to inhabit macroalgal substrates of matching background, while D individuals are evenly distributed between habitats. Unlike D shrimps, H morphs are capable of color change within a few days, but camouflage efficiency is habitat‐dependent. Pink (P) animals collected in the red algal Galaxaura turned cryptic when supplied the brown weed Sargassum, but color change of greenish‐brown (GB) shrimps from Sargassum did not fully conceal in Galaxaura. Homogeneous GB and disruptive morphs select Sargassum, while no preference was detected for homogeneous P individuals. Crypsis efficiency and habitat selection explain the much higher shrimp density in Sargassum compared to Galaxaura. The overall population sex‐ratio did not depart from the 1 : 1 ratio, but D individuals were mostly males and H shrimps chiefly females. These main morphs also differ in shape; D shrimps are more streamlined and H ones stouter, further suggesting enhanced mobility and substrate fidelity, respectively. Morph‐specific functional roles would promote lower density and stable population dynamics at mixed algal beds, but higher density and a more fluctuating trend in monospecific Sargassum stands.
Adult conspecific cues affect molting rate, survival and claw morphology of early recruits of the shore crab Carcinus maenasPDF
Besides signaling adequate benthic habitat, conspecific cues often shorten development time to metamorphosis and affect both survival and growth of early juvenile stages. However, aggregation of juvenile cohorts in preferred habitat, usually biogenic substrates holding intricate physical structure and high food supply, may lead to strong intraspecific competition and cannibalistic interactions. Using a simple laboratory experiment and the crab species Carcinus maenas as a biological model, we investigated the effects of cues released by adults on intermolt time, growth, and survival of conspecific megalop larvae and juveniles. Using geometric morphometric analyses, we also compared the size and shape of the carapace and claw of stimulated (St) and control (C) juveniles at both the 1st (J1) and 5th (J5) benthic stages. Results obtained showed that conspecific cues can reduce significantly intermoult time and survival, but these differences are restricted to some specific stages. Neither the size nor the increment at molt differed between treatments. There were no differences of carapace characteristics, but conspecific cues affected claw size and shape of J1 and J5 individuals, respectively. For J1 crabs, claws of St individuals were larger than those of C ones, showing an initial size effect. In the case of J5 juveniles, there were no size differences but evident morphological differences suggest that St crabs bear stronger chelae. By the J5 stage, both St and C juveniles exhibit initial heterochely which precedes the prevailing adult pattern. In spite of reducing survival rate, we conclude that overall effects of conspecific cues are positive. Stimulated juveniles may attain a size-refuge from cannibalism earlier than C individuals, and are likely to more efficiently use valuable feeding resources demanding crushing power, such as mollusk prey, in habitat patches characterized by high density of benthic consumers where competitive interactions are very likely.