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aestivating snails  aestivating  aestivation  extinct  high temperatures  loss  males  mating  sites  snails  species  sperm  water loss  water 
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Preview: Journal of Molluscan Studies - Advance Access

Journal of Molluscan Studies Advance Access

Published: Fri, 23 Feb 2018 00:00:00 GMT

Last Build Date: Fri, 23 Feb 2018 07:49:38 GMT


Seeking refuge in subsurface microhabitats during aestivation aids avoidance of lethally high temperature and desiccation in the snail Helminthoglypta tudiculata (Binney, 1843) (Pulmonata: Helminthoglyptidae)

Fri, 23 Feb 2018 00:00:00 GMT

The threats to aestivating land snails posed by extremely high temperatures and prolonged desiccation are poorly understood. In this study, we used the southern California native snail Helminthoglypta tudiculata to investigate the role of microhabitat selection in avoiding lethally high temperatures during aestivation. We also examined water loss and metabolism during aestivation to understand the potential limits of water and carbon reserves for aestivating snails. In the field, searches were carried out both on the substrate surface (SS) and in subsurface refugia (SR) such as soft substrate, rodent holes or under rocks. All aestivating snails and the great majority of empty shells found in the field were in SR. In the laboratory, the lethal temperature for active snails in a 1-h exposure was 41.3 ± 0.24 °C. Daily temperature highs measured over a 46-d period from September 2014 to November 2014 exceeded 41.3 °C at all 11 SS sites examined, but in only two of eight SR sites. SR aestivation sites provide protection from lethally high temperatures and water loss. Laboratory measurements of water loss rates for aestivating snails under standardized conditions indicated that, in the field, long-term water loss amounts to c. 244 μg H2O h−1. This loss rate is greater than that needed to ensure survival in the wild, suggesting that laboratory investigations of losses need to be regarded with caution. Measured CO2 fluxes in aestivating snails showed alternating periods of negligible flux punctuated by sharp increases, presumably coinciding with opening of the pneumostome, and decreased exponentially throughout aestivation. Water flux did not co-vary significantly with CO2 flux, indicating that the epiphragm maintains near-saturated humidity in the underlying air space. Water loss was proportionally greater than carbon (CO2) loss in long-term dormancy, suggesting that desiccation poses a greater threat than starvation to aestivating snails. Helminthoglypta tudiculata probably spends >50% of the year in aestivation. Maintaining undisturbed ground surface with diverse refugia for aestivating land snails should be given appropriate priority in conservation efforts.

Spermatophore dimorphism in the chokka squid Loligo reynaudii associated with alternative mating tactics

Wed, 14 Feb 2018 00:00:00 GMT

Chokka squid (Loligo reynaudii) have characteristic alternative mating tactics: ‘consort’ males temporarily pair with and guard a female and transfer spermatophores onto her oviduct opening inside the mantle cavity, whereas ‘sneaker’ males rush towards a mating pair and transfer spermatophores onto the female’s buccal membrane near her sperm storage organ. Differences in mating behaviours and their related sperm-storage sites clearly constrain the fertilization process and can drive dimorphism between consort and sneaker males. The presence and character of male dimorphism has not yet been fully examined in this species, but consort males are commonly much larger than sneaker males. We observed clear dimorphism in spermatangia (the sperm mass ejaculated from the spermatophore), consistently associated with the two alternative sperm storage sites on the female’s body. Observations of spermatophores stored in the Needham’s sac of mature males confirmed that small males produce ‘sneaker-type’ spermatangia whereas larger males produce ‘consort-type’ spermatangia, and no individuals possessed both types. Therefore, by association, the mating tactic adopted (including the sperm deposition site used) by individual males can be determined from observation of their spermatangial type, without requiring direct behavioural observation of mating. This ability to infer information about mating tactic will improve our understanding of the reproductive system and mating dynamics in this species.

Genetic and morphometric rediscovery of an extinct land snail on oceanic islands

Wed, 14 Feb 2018 00:00:00 GMT

Confirming the extinction of species with only old occurrence records is often difficult, due to the scarcity of biological information. Phylogenetic position and taxonomic status of the potentially extinct species are unclear in most such cases. In the present study, we document that a species of the endemic genus Hirasea of the oceanic Ogasawara Islands, which was formerly believed to have become extinct, still survives, on the basis of combined surveys involving molecular phylogenetics and morphometrics. Hirasea is notorious for its highly diversified shell morphologies and a number of species and subspecies have already become extinct because of environmental changes and impacts of alien predators. In this study, we first reconstruct phylogenetic relationships among extant Hirasea populations. Next, on the basis of quantitative shell morphological analysis of extant populations and type specimens, we identify morphological traits that reflect phylogenetic relationships among the species. By using these morphological traits and molecular phylogenies, we demonstrate that H. nesiotica liobasis, previously considered extinct, is still extant on Chichijima. Although classifications by means of morphology and molecular phylogeny often show incongruences, judgement of the conspecific status of living and extinct populations is still possible by considering ranges of variation and phylogenetic constraints on morphological traits.