Monthly Archives: September 2014

Cerion ABC

One of my first sights of Neotropical land snails were very large bottles full of Cerion shells from Curaçao in the lab of the late P. Wagenaar Hummelinck. Willy de Vries, who worked at the same period in the lab, studied these shells from Aruba, Bonaire and Curaçao (in Dutch ‘ABC islands’) by taking various measurements on hundreds of shells. I recall her to be disappointed to conclude that “no obvious geographic variation in Cerion uva exists” (de Vries, 1974). This contrary to H.B. Baker, who had described various subspecies from the islands, and had concluded that Curaçao has western, central and eastern faunal regions (Baker, 1924). Wagenaar Hummelinck (1990), however, rejected this hypothesis and concurred with Gould’s (1969) partition of Curaçao in a western and eastern region.

Harasewych2014_f2

Harasewych has now published a nice paper restudying the Cerions from these islands using molecular data (Harasewych, 2014). The abstract reads: “The systematic relationships of the Cerion uva complex and its constituent taxa are reviewed based on partial sequences of the cytochrome c oxidase I and 16S rDNA genes from 19 populations spanning the geographic range of the species complex and including the type localities of 8 of the 9 subspecies and forms. Molecular data support the conclusion of prior morphometric studies that all living Cerion inhabiting Aruba, Curaçao and Bonaire are members of a single species, C. uva. Sequence variability among and within populations is not sufficiently discontinuous to segregate populations into discrete, specieslevel taxa. Three of four subspecies, proposed on the basis of geographic isolation during the Quaternary, C. uva uva (Linnaeus, 1758), the nominotypical subspecies from eastern Curaçao, C. uva knipensis Baker, 1924, from western Curaçao, and C. uva bonairensis Baker, 1924, from Bonaire, are all supported by distinctive haplotypes. Cerion uva arubanum Baker, 1924, a taxon based on living specimens from Aruba, is shown to be a synonym of C. uva uva, with which it shares a preponderance of haplotypes. It is conjectured that C. uva was widespread on Aruba during the Quaternary, but had become extinct on that island, and was reintroduced from a population near Willemstad in eastern Curaçao by humans (either by Caquetío Indians or by European settlers) within the past 800 years. Further investigation is needed to determine if Quaternary Aruban Cerion warrant subspecific recognition. On the island of Curaçao, molecular data lend support to the partition of the Cerion fauna into C. uva knipensis, which is confined to an isolated western region, as defined by Baker, and C. uva uva, which inhabits a broad, eastern region that is composed of Baker’s central and eastern regions. A population at Ronde Klip in eastern Curaçao has remained genetically isolated, and retains subspecific status as C. uva diablensis Baker, 1924. A neotype is designated for Turbo uva Linnaeus, 1758, as is necessary to provide an objective standard of reference for this species-group taxon, and for the genus- and family-level taxa based upon it.”

Harasewych2014_f7

References:

Baker, H.B., 1924. Land and freshwater molluscs of the Dutch
Leeward Islands. – Occasional papers of the Museum of Zoology.
University of Michigan 152: 1–160.
Gould, S.J., 1969. Character variation in two land snails from the
Dutch Leeward Islands: geography, environment, and evolution. –
Systematic Zoology 18: 185–200.
Harasewych, M.G., 2014. Systematics and phylogeography of Cerion sensu stricto (Pulmonata: Cerionidae) from Aruba, Curac¸ao and Bonaire. – Journal of Molluscan Studies (Advance Access): 1–19.
Vries, W. de, 1974. Caribbean land molluscs: notes on Cerionidae. –
Studies on the Fauna of Curac¸ao and other Caribbean Islands 45: 81–117
Wagenaar Hummelinck, P., 1990. About the malacological
subdivision of Curac¸ao; a review. – Contributions to Zoology 60: 181–187.

Genetics of invasive Cornu

Another paper on invasive species, i.e. Cornu aspersum in Chile, is entirely devoted to genetics. It was recently published by Nespolo et al. (2014).

Nespolo2014_Fig2

The summary of this paper comprises seven items:
1. The distribution of additive vs. non-additive genetic variation in natural populations represents a central topic of research in evolutionary/organismal biology. For evolutionary physiologists, functional or whole-animal performance traits (‘physiological traits’) are frequently studied assuming they are heritable and variable in populations.
2. Physiological traits of evolutionary relevance are those functional capacities measured at the whole-organism level, with a potential impact on fitness. They can be classified as capacities (or performances) or costs, the former being directly correlated with fitness and the latter being inversely correlated with fitness (usually assumed as constraints).
3. In spite of their obvious adaptive significance, the additive genetic variation in physiological traits, and its relative contribution to phenotypic variance (or narrow-sense heritability) in comparison with maternal, dominance or epistatic variance, is known only for a few groups such as insects and mammals.
4. In this study, we assessed the additive and maternal/non-additive genetic variation in a suite of physiological and morphological traits in populations of the land snail Cornu aspersum.
5. Except for dehydration rate (h2 = 0.32 +/- 0.15), egg mass (h2 = 0.82 +/- 0.30) and hatchling mass (h2 = 1.01 +/- 0.31; population = fixed effect), we found very low additive genetic variation. Large non-additive/maternal effects were found in all traits. Cage effects did not change the results, indicating low contribution of common environmental variance to our results. No differences were found between the phenotypic and non-additive genetic variance/covariance matrices.
6. Even though we compared populations across 1300 km in a common garden set-up, our results suggest an absence of physiological as well as morphological differentiation in these populations.
7. These results contrast with previous analyses in the original distributional range of this species, which found high additive genetic variation in morphological traits. These are intriguing results demanding further quantitative genetic studies in the original distributional range of this species as well as the history of colonization of this invasive species.

Especially items 6 and 7 are interesting. Suppose we may see some time a follow-up by these authors.

Reference:

Nespolo, R.F., Bartheld, J.F., González, A., Bruning, A., Roff, D.A., Bacigalupe, L.D. & Gaitan-Espitia, J.D., 2014. The quantitative genetics of physiological and morphological traits in an invasive terrestrial snail: additive vs. non-additive genetic variation. – Functional Ecology 28 (3): 682-692.

Invasive Deroceras slugs

Just published: a paper by Hutchinson et al. (2014) on invasive Deroceras slugs. The abstract reads:

The article reviews distribution records of Deroceras invadens (previously called D. panormitanum and D. caruanae), adding significant unpublished records from the authors’ own collecting, museum samples, and interceptions on goods arriving in the U.S.A. By 1940 D. invadens had already arrived in Britain, Denmark, California, Australia and probably New Zealand; it has turned up in many further places since, including remote oceanic islands, but scarcely around the eastern Mediterranean (Egypt and Crete are the exceptions), nor in Asia. Throughout much of the Americas its presence seems to have been previously overlooked, probably often being mistaken for D. laeve. New national records include Mexico, Costa Rica, and Ecuador, with evidence from interceptions of its presence in Panama, Peru, and Kenya. The range appears limited by cold winters and dry summers; this would explain why its intrusion into eastern Europe and southern Spain has been rather slow and incomplete. At a finer geographic scale, the occurrence of the congener D. reticulatum provides a convenient comparison to control for sampling effort; D. invadens is often about half as frequently encountered and sometimes predominates. Deroceras invadens is most commonly found in synanthropic habitats, particularly gardens and under rubbish, but also in greenhouses, and sometimes arable land and pasture. It may spread into natural habitats, as in Britain, South Africa, Australia and Tenerife. Many identifications have been checked in the light of recent taxonomic revision, revealing that the sibling species D. panormitanum s.s. has spread much less extensively. A number of published or online records, especially in Australia, have turned out to be misidentifications of D. laeve.

HutchingtonFig4

Reference:

Hutchinson, J., Reise, H. & Robinson, D., 2014. A biography of an invasive terrestrial slug: the spread, distribution and habitat of Deroceras invadens. NeoBiota 23: 17–64. Available at http://neobiota.pensoft.net/articles.php?id=4006.