The diets of juvenile horseshoe crabs,Tachypleus tridentatus and Carcinoscorpius rotundicauda (Xiphosura), from nursery beaches proposed for conservation in Hong Kong

Once common as a fishery resource, adult horseshoe crabs of two species occur in Hong Kong. A third, Tachypleus gigas, can no longer be found. Once common too were breeding and nursery beaches for horseshoe crabs in Hong Kong but overfishing of adults, pollution and coastal reclamation have reduced these to but three identified sandy mudflats and only one where juvenile Tachypleus tridentatus and Carcinoscorpius rotundicauda are sympatric. Nothing is known, however, of the conservation requirements of these two species locally and this study of the diets of these juvenile horseshoe crabs on two such nursery beaches aimed at providing information on this most elementary aspect of their biology. Gut contents of juvenile horseshoe crabs, i.e. nine Tachypleus tridentatus (8.5–67?mm prosoma width) and two Carcinoscorpius rotundicauda (50 and 52?mm prosoma width), were analysed and compared with the composition of the ambient assemblage of meiobenthos on a nursery beach at Pak Nai, Hong Kong. The obtained data suggest that juvenile horseshoe crabs of both species are selective benthic feeders and subsist mainly on insect larvae, polychaetes, oligochaetes, small crabs and thin-shelled bivalves. A strong, positive, preference for insect larvae (Chironomous sp.: Diptera: Chironomidae) was recorded, but with no preference for meiofauna over macrofauna.     

The morphological differentiation of two horseshoe crab species,Tachypleus tridentatus and Carcinoscorpius rotundicauda (Xiphosura), in Hong Kong with a regional Asian comparison

Two horseshoe crab species, namely Tachypleus tridentatus and Carcinoscorpius rotundicauda, have been identified from Hong Kong. This paper describes the morphological characteristics of the two species and the morphometrics employed to help distinguish them. Comparisons were also made between adults from local waters and those from other Asian geographic regions. Intra-specific variations were also investigated by comparing morphological data obtained for local T. tridentatus juveniles and individuals of comparable sizes from Fujian Province, China. Morphological differences between the species and sexes and significantly different morphometric ratios were identified for the two horseshoe crab species. Intra-specific variations in morphometric characteristics were also demonstrated between juveniles from local beaches and those from Fujian.     

Population structure and breeding biology of the hairy crab Pilumnus vespertilio (Fabricius, 1793) (Crustacea: Brachyura: Pilumnidae) in southern Mozambique

The population structure and reproduction of Pilumnus vespertilio were studied for the first time in Mozambique. Random samples of crabs were taken monthly from January to December 2002 from a pebble area of Inhaca Island, southern Mozambique. A clear sexual dimorphism was observed in the present population with males reaching greater sizes than females. Sex ratio was female‐biased, and the monthly size–frequency distributions were often bimodal. The annual reproductive cycle of Pilumnus vespertilio was continuous with peaks of breeding in summer. Results suggest that embryonic development may be synchronized within the population as a result of the very high reproductive activity observed in summer. Juveniles are recruited mostly in winter in the study area.     

Population structure and breeding season of the hermit crab Diogenes brevirostris Stimpson, 1858 (Decapoda,Anomura, Diogenidae) from southern Mozambique

In this study the population dynamics of the diogenid hermit crab Diogenes brevirostris is evaluated focusing on size structure, sex ratio and breeding season. Crabs were randomly taken on a monthly basis from January to December 2003 at Costa do Sol, Maputo Bay, southern Mozambique. A total of 622 crabs was obtained of which 290 were males (46.6%), 170 were non‐ovigerous females (27.3%) and 162 were ovigerous females (26.1%). The overall size frequency distribution was unimodal for males, non‐ovigerous females and ovigerous females. The overall sex ratio (1:1.15) differed from the expected 1:1 ratio. Sexual dimorphism was evidenced by the larger size attained by males in relation to both ovigerous and non‐ovigerous females. Breeding took place year‐round with three peaks of spawning (March, August and December). Despite the high reproductive activity, young recruits were scarce in the population. The present results suggest that the study area is suitable for reproduction and growth whereas recruitment may take place in different areas from that occupied by the adults.     

Population structure and reproductive biology of the fiddler crab Uca urvillei (Brachyura: Ocypodidae) in Maputo Bay (south Mozambique)

Although fiddler crabs are among the main faunal components in mangrove habitats, few studies have described the population structure and reproduction of tropical species. Such information is important for understanding their life cycle and ecology. In this study, the population structure and reproduction of Uca urvillei were studied at Costa do Sol, a tropical mangrove forest in Maputo Bay, southern Mozambique. Ten 1.0‐m² squares were sampled during low tide periods, between January and December 2003. The population is characterized by normal size distributions, which are slightly skewed to the left. Males on average are larger than females. Males were more abundant than females and the monthly sex ratios were male‐biased. Juveniles were found year‐round but were less common in June and December. Both gonadosomatic index and frequency of ovigerous females showed that Uca urvillei breeds continuously with peaks in summer and a strong decrease in winter. Egg number was proportional to female size.     

The Sex Ratio of Orange-flanked Bush-robins (Aves: Passeriformes: Muscicapidae) from a Winter Population in Central China

The sex ratio of a population is an important demographic parameter, but compared with breeding populations, the sex ratios of avian winter populations have received relatively little attention. The orange-flanked bush-robin (Tarsiger cyanurus) is a migratory species whose plumage is sexually dimorphic with delayed plumage maturation wherein first-year males show female-like plumage. We investigated the sex ratio of an orange-flanked bush-robin population wintering in Dongzhai National Nature Reserve located in central China. The results show that most (> 85%) orange-flanked bush-robins of this population have female-like plumage, implying that the population sex ratio might be female-biased. However, genetic analysis revealed that most (c. 70%) individuals with female-like plumage were males, resulting in a significantly male-biased population sex ratio. Among the individuals with female-like plumage, the males were found to have significantly longer wings and tails than females, but the accuracy of a discriminant analysis employing the two morphological traits to sex them was low. The results suggest that a genetic method is a more appropriate way to sex those orange-flanked bush-robins with female-like plumage and more importantly, one needs to be cautious when using the morphology of individuals to infer the sex ratio of a population for species like orange-flanked bush-robins.     

Environmental influences on movements and distribution of a wild horse (Equus caballus) population in western Nevada,USA: a 25-year study

Wild horse populations in the American West have been heavily managed to regulate horse numbers since the inception of the Free-Roaming Wild Horse and Burro Act of 1971. The Montgomery Pass Wild Horse Territory (MPWHT) on the California/Nevada border is unique in the absence of human intervention there across the past 30 years. This has provided the opportunity to observe long-term patterns in the natural relationship between wild horses and their environment and to examine environmental impacts on the horse population and its activities, movements and distribution on the range. In this study multiple variables in the physical environment and in horse behaviour were monitored seasonally across 25 years beginning in 1987. Distinct summer (higher elevations) and winter (lower elevations) range use was characteristic for more than 60% of the population during the first 7 study years, with subsequent gradual but marked reduction in use of summer range. While approximately 20% of the population continued to annually use the historical summer range, the majority divided into two geographically and functionally separate subpopulations that resided year round in the historical winter range and adjacent areas on opposite sides of the MPWHT. Mountain lion predation on foals was restricted to the summer range, and exodus of horses from the summer range resulted in increased foal survival where horse subpopulations eventually resided. The long-term consequences of increased horse numbers in the MPWHT remain under continued study. The present study has shown that wild horses are highly adaptive and individually varied in response to environmental pressures. It has also demonstrated the value of long-term monitoring of wild horse populations to reveal underlying dynamics and their potential management implications.     

The occurrence of facultative paedomorphosis in a lacustrine population of the Pyrenean newt (Calotriton asper): morphology and age structure

Facultative paedomorphosis is a common polyphenism in newts where two alternative phenotypes can coexist: metamorphs and paedomorphs (mature with larval traits, i.e. retaining gills). This phenomenon has been reported in some lacustrine populations of the Pyrenean newt (Calotriton asper). The morphology and life-history traits were studied in a lacustrine population of this species with the occurrence of facultative paedomorphosis. The results showed that 24.3% of adults retained gills at different levels of reabsorption and had a smoother skin compared with the other populations, which were fully metamorphic. The body size and shape showed significant sexual differences, with males being larger than females. The presence of paedomorphic traits also affected the body size and shape, revealing a complex pattern of growth in which metamorphic adults were larger than paedomorphs. The age structure was different between sexes, with a median age of 10.5 and 7 years and longevity of 19 and 14 years in males and females, respectively. Considering each sex separately, the age structure was not significantly different between metamorphic and paedomorphic newts. In addition, metamorphosed and branchiate juveniles were found with a maximum age of 13 and 20 years, respectively. Remarkably, long-lived larvae with an exceptional individual of 18 years were found, which has not previously been reported in any other newt species. The mechanisms that can explain the evolution of paedomorphosis are complex and comprise the interaction of multiple factors related to the cost of reproduction and growth.     

Cercaria hastata sp. nov. (Digenea: Trematoda) in Bullia digitalis,a sandy beach surfing whelk from the Western Cape coast of South Africa: epidemiology and sex linked phenomena

Morphometric and sex linked phenomena in male Bullia digitalis, from the Western Cape coast of South Africa, are related to infection with a digenean microphallid larva described here for the first time and named Cercaria hastata. Penis shedding in Bullia is not uncommon. Most of the stumps are found on infected whelks, and this is probably due to parasitic inhibition of an otherwise rapid regeneration. The infection also abolishes sperm production. Stumps were never seen on sperm producing males, all of which have large penes, and in non-infected males, shedding occurs only in non-producers. In large non-infected Bullia, those which have underdeveloped penes and are non-producers of sperm may be transient intersexes. This is supported by the exhibition of protandry indicators such as brooding, nonsize preferential mate selection and gregariousness. Infection prevalence is size dependent, large whelks being more commonly infected; but parasitic gigantism is thought unlikely as Bullia is iteroparous.