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Two forms of the squat lobster Pleuroncodes monodon can be found along the Pacific coast of South America: a smaller pelagic and a larger benthic form that live respectively in the northern and southern areas of the geographic distribution of the species. The morphological and life history differences between the pelagic and benthic forms could be explained either by genetic differentiation or phenotypic plasticity. In the latter case it would correspond to a heterochronic phenotypic plasticity that is fixed in different environments (phenotype fixation). The aim of this study was to evaluate whether the two forms are genetically differentiated or not; and thus to infer the underlying basis-heritable or plastic-of the existence of the two forms. Based on barcoding data of mitochondrial DNA (the COI gene), we show that haplotypes from individuals of the pelagic and benthic forms comprise a single genetic unit without genetic differentiation. Moreover, the data suggest that all studied individuals share a common demographic history of recent and sudden population expansion. These results strongly suggest that the differences between the two forms are due to phenotypic plasticity.

The metazoan parasite fauna of Hippoglossina macrops (n = 123) from northern Chile (30°S)

The growth rate, reproductive aspects, and natural mortality of chimaeras and ratfish are poorly known. In this study, life-history parameters for cockfish Callorhinchus callorhynchus (Holocephali-Callorhinchidae) are estimated, which is an important fish resource exploited in Chile. Specimens were sampled from the artisanal fishery captures, from November 2006 to November 2007. The standard length (SL) of males fluctuated between 20 and 62 cm, and between 21 and 70 cm for females. Von Bertalanffy growth parameters were estimated through length-frequency data analysis using MULTIFAN. The length-weight relationship and von Bertalanffy growth parameters were significantly different for males and females, as well as the length at 50% maturity. For males a model with 5 age-classes was the best, with asymptotic length L ∞ =52 cm SL, growth coefficient K=0.473 yr −1 , and age at length zero t 0 =−0.690 yrs. For females the best model was represented by 10 age-classes (L ∞ =70.3 cm SL, K=0.193 yr −1 , t 0 =−1.158 yrs) in the lengthfrequency data sets. Length at 50% maturity of males was estimated in 43.7 cm SL, and in 50.2 cm SL for females. The natural mortality rate fluctuated between 0.42 and 0.82 yr −1 for males and between 0.12 and 0.37 yr −1 for females, depending upon the method used. It is concluded that C. callorhynchus is a species with lifehistory parameters significantly different between males and females, and such differences should be taken into account in future population dynamics analysis.