Conspecific cues affect stage-specific molting frequency, survival, and claw morphology of early juvenile stages of the shore crab Carcinus maenas

Benthic conspecific cues are used by competent larvae of many marine invertebrates to locate and settle on suitable habitat. However, aggregations of conspecifics can generate strong intraspecific competition and inter-cohort cannibalism. We investigated the effects of adult conspecific cues on general fitness parameters of juvenile Carcinus maenas (stages J1-J5), and used geometric morphometrics to investigate patterns of allometric growth indicative of life-history strategies and resource use potential. Cues induced faster metamorphosis and slightly shortened intermolt time in J2 individuals, at the expense of acute mortality in J1 crabs. These effects are cumulative but compensatory processes nullify differences by the end of the experiment. Allometric carapace change toward the adult standard remained unchanged, but conspecific cues induced first a change in size (J1) and then in shape (J5) of claws. In both control and cued juveniles, heterochely was incipient but apparent in J5 crabs. Independently of body side, conspecific cues triggered a very marked increase of the propodus posterior margin, presumably enhancing general strength. Therefore, early benthic stages may grow slightly faster to a size refuge, and develop stronger claws providing competitive advantage for the use of high-value food items when population density-dependent processes are more probable

The effects of scaling on age, sex and size relationships in Red-legged Partridges

Wild birds differ in size according to their age and sex, adult birds being larger than juveniles. In the galliforms, males are larger than females, in contrast to some groups, such as the raptors, in which the females are larger. Size generally influences the rank hierarchy within a group of birds, although the age, sex, temperament and behaviour of an individual may override its size related rank order. The scaled size of birds according to age and sex affects their physiology and behaviour. Precise details of body-size differences by age and sex are poorly known in most partridge species. We measured 13,814 wild partridges in a homogenous population over 14 years of study to evaluate size differences within a uniform habitat and population management regime. We show that wild Red-legged Partridges have scaled mass, and body- and wing-lengths consistent with age/sex classes. Power functions between mass and body-length (as a proxy for walking efficiency), and between mass and wing-length (for flight efficiency) differ between juvenile females and males, and adult females and males. We discuss these findings and their physiological, behavioural and ecological implications.A.M. was supported by a Ramón y Cajal research contract by the Ministry of Economy and Competitiveness (RYC-2012-11867).Peer reviewe