Evidence for a single panmictic and genetically diverse population of the coconut crab Birgus latro (Decapoda: Anomura: Coenobitidae) on Christmas Island in the Indian Ocean

Abstract

For the coconut crab Birgus latro, Christmas Island in the Indian Ocean may be one of the last retreats where populations of this declining species are not threatened by overharvesting, as on many other mostly tropical Indo-Pacific islands within the species’ wide range. Nevertheless, the population on Christmas Island has experienced severe losses during the past decade owing to habitat destruction and road mortality. To assess the population’s evolutionary potential and identify the number of conservation units, we conducted a combined morphometric and population genetic analysis using microsatellite markers. The findings suggest that the population is genetically diverse and panmictic. Neither genetic nor morphometric analyses revealed any population substructuring. There was no genetic evidence for sex-biased dispersal. Single-sample estimators for the effective population size (Ne) ranged from 492 to infinity, with very wide confidence intervals; they should therefore be viewed with caution. It would be advisable to reanalyse Ne, preferably by temporal methods. Despite mixed results, there is stronger evidence against rather than for the occurrence of a recent genetic bottleneck. So far, the population of B. latro on Christmas Island may be considered as a single conservation management unit, this way simplifying future conservation efforts taken for this magnificent species.

Ecological studies on the hermit crab Calcinus latens (Paguroidea: Diogenidae), from Aqaba Gulf, Egypt; Part (II), some morphological aspects of intersexuality phenomenon

“…Those findings indicate sexual dimorphism in size (Sl), shield width, wet weight, left chela size (represented by LpL and LpH) and right chelar propodus length in C. latens. Sexual dimorphism was recorded in chela size and in cephalic shield length, weight and cheliped size in the hermit crabs, Calcinus tibicen and Birgus latro respectively, with males being larger than females in those dimensions (Fransozo et al, 2003 &Anagnostou andSchubart, 2014). The degree of sexual dimorphism regarding the crab weight was higher than that regarding the other measured body dimensions in the present study.…”

“…Checking the normality of the data and the standardization of the measured chelar propodi dimensions (LpL, LpH and RpL) were done to study relative growth and heterochely during carrying out the above mentioned part I by Abd El-Wakeil et al (in progress). That standardization was done using the equation applied by Anagnostou & Schubart (2014). Data checking for normality was done using Shapiro-Wilk tests through the SPSS program (PASW Statistics 18).…”

“…Males represented the larger sex while females represented the smaller one. Thus, the compressed size dimorphism index (SDI) and the degree of size dimorphism (SD [%]) were calculated by the same formulae applied by Anagnostou & Schubart (2014) as follows. The SDI was calculated by the formula, -[( mean size of males/ mean size of females) -1].…”

A Mighty Claw: Pinching Force of the Coconut Crab, the Largest Terrestrial Crustacean

“…A morphological study of coconut crabs in Christmas Island, Indian Ocean, identified sexual dimorphism in chelae size and heterochely [15]. This study shows that the pinching forces of males and females might be expected to differ.…”

Morphometric differentiation among populations of Leptodius exaratus (H. Milne Edwards, 1834) (Brachyura, Xanthidae) from the Persian Gulf and the Gulf of Oman

“…This might suggest a refuge-defence polygenic mating, like in the case of Xantho poressa (Olivi, 1792) (see Spivak et al, 2010). Male-biased sexual size dimorphism (SSD) is due to sexual selection where bigger male specimens have the higher chance of reproduction Anagnostou & Schubart, 2014). Leptodius exaratus was mainly found on shores with rockycobble substrate.…”