17 research outputs found
Reconciling Deep Calibration and Demographic History: Bayesian Inference of Post Glacial Colonization Patterns in Carcinus aestuarii (Nardo, 1847) and C. maenas (Linnaeus, 1758)
A precise inference of past demographic histories including dating of demographic events using Bayesian methods can only be achieved with the use of appropriate molecular rates and evolutionary models. Using a set of 596 mitochondrial cytochrome c oxidase I (COI) sequences of two sister species of European green crabs of the genus Carcinus (C. maenas and C. aestuarii), our study shows how chronologies of past evolutionary events change significantly with the application of revised molecular rates that incorporate biogeographic events for calibration and appropriate demographic priors. A clear signal of demographic expansion was found for both species, dated between 10,000 and 20,000 years ago, which places the expansions events in a time frame following the Last Glacial Maximum (LGM). In the case of C. aestuarii, a population expansion was only inferred for the Adriatic-Ionian, suggestive of a colonization event following the flooding of the Adriatic Sea (18,000 years ago). For C. maenas, the demographic expansion inferred for the continental populations of West and North Europe might result from a northward recolonization from a southern refugium when the ice sheet retreated after the LGM. Collectively, our results highlight the importance of using adequate calibrations and demographic priors in order to avoid considerable overestimates of evolutionary time scales
Interspecific Hybridization and Mitochondrial Introgression in Invasive Carcinus Shore Crabs
Interspecific hybridization plays an important role in facilitating adaptive
evolutionary change. More specifically, recent studies have demonstrated that
hybridization may dramatically influence the establishment, spread, and impact
of invasive populations. In Japan, previous genetic evidence for the presence of
two non-native congeners, the European green crab Carcinus
maenas and the Mediterranean green crab C.
aestuarii, has raised questions regarding the possibility of
hybridization between these sister species. Here I present analysis based on
both nuclear microsatellites and the mitochondrial cytochrome C oxidase subunit
I (COI) gene which unambiguously argues for a hybrid origin of Japanese
Carcinus. Despite the presence of mitochondrial lineages
derived from both C. maenas and C. aestuarii,
the Japanese population is panmictic at nuclear loci and has achieved
cytonuclear equilibrium throughout the sampled range in Japan. Furthermore,
analysis of admixture at nuclear loci indicates dramatic introgression of the
C. maenas mitochondrial genome into a predominantly
C. aestuarii nuclear background. These patterns, along with
inferences drawn from the observational record, argue for a hybridization event
pre-dating the arrival of Carcinus in Japan. The clarification
of both invasion history and evolutionary history afforded by genetic analysis
provides information that may be critically important to future studies aimed at
assessing risks posed by invasive Carcinus populations to Japan
and the surrounding region
Effects of ablation of Y organs and regeneration on ecdysteroid levels and development of the crab, pilumnus hirtellus (xanthidae)
Seasonal variations and the role of neurosecretory hormones on the androgenic gland of the prawnMacrohrachium lamerrii
Limb-loss in pond-reared blue swimmer crabs Portunus pelagicus (L.): Effect on growth in an indoor shedding system
Limb-loss in crustaceans can reduce moult increment and delay or advance the timing of moulting, both aspects that are likely to impact upon soft-shell crab production. Pond-reared blue swimmer crabs Portunus pelagicus were harvested and maintained in a crab shedding system. The wet weight, carapace width (CW) and the occurrence of limb-loss were assessed before stocking in the shedding system and after each of the next three moults. Many of the crabs were initially missing one or two limbs and these did not grow as much as the crabs that were intact at the start of the trial. Despite its strong correlation with wet weight, CW changes proved to be misleading. Limb-loss reduced the %CW increment but not the per cent weight increment (where the later is calculated from the actual pre-moult weight). Pre-moult weight explained much of the variation in post-moult weight, with crabs moulting to approximately double their weight. Limb-loss reduced 'growth' and production from the pond because it reduced pre-moult weight but limb-loss did not alter the weight change on shedding a given weight of crabs, although some of that change now included regeneration of limbs. One can hypothesize that much of the size variation seen in pond-reared crabs may be due to accumulated effects of repeated limb-loss, rather than genetic variation