Monthly Archives: July 2018

Snails and forest relicts in Chile

Freshly pressed: a paper by Francisco Cádiz and co-authors describing how they used land snails to decipher the origin and isolation in forest relicts in northern Chile.

The abstract reads: “Among the questions surrounding the biogeographical history of the Chilean biota, none has gathered more interest than the origin of the Fray Jorge (FJ) for- est relict and its biota. Inserted in a semi‐desert area, this forest enclave exists due to the existence of a very particular microclimate in this region. The age of the disjunction and the historical relationship between the FJ biota with the remaining components of South America are explained by two distinct, competing hypotheses: the first suggests that it would have become isolated during the climatic changes of the Paleogene/Neogene, while the second suggests that the isolation is a product of Quaternary glaciations. To discriminate between these competing hypotheses, we used DNA sequence phylogeny methods and molecular genetic dating to the study of a genus of land snails (Plectostylus) that occurs in the FJ relict and throughout Chile. The phylogeny shows a clear distinction between forest and arid clades, and each of these clades is formed by many geographically circumscribed populations. The FJ fragment snails form a clade that is sister to all other forest clades. The separation between the Fray Jorge clade and the other forest clades dates back to the Paleogene/Neogene. Our data suggest that the FJ forest is a relict from the forests that occupied that landscape during the Paleogene/Neogene and retreated due to the aridification of the region. We also observe that the current taxonomy of the Plectostylus genus must be re‐evaluated”.

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An interesting paper that uses molecular data of an endemic land snail group to sort out competing hypotheses of ancient landscape genesis. More often, ecological data are used to support a hypothesis of the taxonomy of species; this time it is the other way around. While working on this study the authors also collected data on the taxonomy of this group, but this will be dealt with in a future paper.

Reference:
Cádiz, F.J. et al., 2018. Phylogeography of Plectostylus Beck, 1837 (Gastropoda, Stylommatophora: Orthalicoidea): Origin and isolation of the Fray Jorge forest relicts in northern Chile. – Journal of Zoological Systematics and Evolutionary Research, doi: 10.1111/jzs.12241 (10 pp.) (advance publication).

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Xolotrema and the collation of Ferussac’s ‘Histoire naturelle…’

Harry Lee regularly adds insightful tidbits which go way beyond the limited distribution of the home-made journal in which he publish them. One such tidbit is the correct publication date of a Polygyrid snail occurring in Florida and described by Férussac. While has has struggled to get everything right, he now presents an updated collation of Férussac’s Histoire naturelle…, which deserves a wider audience. Reason why I copy his whole article here in this blogpost.

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Reference:
Lee, H.S., 2018. Xolotrema denotatum (Férussac, 18xx), its iconography and taxonomy – resolution. – Shell-O-Gram, 59 (4):2-4.

Taxonomy of Omalonyx

A group of Brazilian authors have made a comprehensive study on the succineid genus Omalonyx, with interesting results.

“The genus Omalonyx d’Orbigny, 1837, includes neotropical semi‐aquatic succineid slugs and comprises six recognized species to date. Field surveys across continental South America recovered five of the six recognized species. According to the morphological characters traditionally included in Omalonyx descriptions, the specimens were tentatively identified as O. matheroni, O. pattersonae, O. convexus, O. geayi and O. unguis. Employing sequences of mitochondrial cytochrome oxidase I (COI) alone or combined with the nuclear second internal transcribed spacer (ITS2) in discovery methods of species delimitation (GMYC and STACEY) led to species delimitation hypotheses that, except for unambiguously supporting O. convexus, have no correspondence to morphologically based assignments. To choose the delimitation model that best fit our data, the hypotheses recovered by GMYC, STACEY and morphology and created by merging species recovered by those methods had their marginal likelihood estimated and compared using the Bayes factors. The best‐supported hypothesis distinguished two species besides O. convexus: one widespread over most of South America and the other restricted to Rio de Janeiro State, Brazil. Furthermore, the pattern of genetic structuring supports pathways connecting the Amazonian and Atlantic forests. This pattern is similar to that observed in terrestrial taxa (e.g., forest‐dwelling small mammals) and is different from the pattern for fully aquatic taxa.”

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This is a well-executed study that uses different methods to formulate several hypotheses. The best-supported one leads the authors to conclude that there are two species to be recognised: O. convexus (Martens, 1868) and O. matheroni (Potiez & Michaud, 1835). This result is interesting, the more since this group is extremely difficult to study using the morphology alone. Such integrative studies are thus the way forward, and should be attempted also for other groups of Neotropical snails.

 

Reference:
Vidigal, T.H.D.A. et al., 2018. Integrative taxonomy of the neotropical genus Omalonyx (Elasmognatha: Succineidae). – Zoologica Scripta, 47 (2): 174-186.

Rediscovery of an achatellinid

Just published by Araya et al., a paper on the rediscovery of an achatellinid snail on Easter Island. The abstract reads: “The achatinellid Pacificella variabilis Odhner, 1922, is reported for the first time since its original description from its type locality, Easter Island (Rapa Nui), South Pacific Ocean, Chile. Specimens were found living on the bark of a lemon tree in Hanga Roa town and among the endemic grass Paspalum forsterianum on Motu Nui Islet. A redescription of the shell based on scanning electron microscopy (SEM) is provided. This represents the first report of the habitat of the species on Easter Island.”

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It always nice to see a rediscovery of a species nearly a century after its initial description 🙂

Reference:
Araya, J.F. et al., 2018. Rediscovery of Pacificella variabilis (Gastropoda: Achatinellidae) on Easter Island. – Pacific Science, 72 (3): 329-334.

Gastropods from Alagoas, Bazil

Just published, a new paper on snails from Alagoas state in northeastern Brazil; surely a place where little malacological research has been done.

The abstract reads: “A thorough collection effort recently took place at Pedra Talhada Biological Reserve (Reserva Biológica de Pedra Talhada, in Portuguese) in Alagoas state, one of the largest fragments of Atlantic Forest in northeastern Brazil. The expedition recovered hundreds of land snails and this material is fully reported and described herein. Forty-two species were found in the reserve (47 counting historical records), comprised mostly of stylommatophoran snails, although some species of Neritimorpha and Caenogastropoda were also found. Many of these species are recorded here for the first time from Alagoas state, extending the geographical range of some or filling distribution gaps of others. The genera Bothriopupa and Sterkia, both vertiginids, are reported here from Brazil for the first time. One important find is Megalobulimus cardosoi, which was deemed extinct in the IUCN Red List. Furthermore, a new species of Charopidae is described, Radiodiscus ubtaoi sp. nov. Despite being a reserve, signs of depredation were observed in Pedra Talhada by our team, underlining the urgency of strengthening and enforcing the protection of this area”.

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The paper contains many good photographs of various snails, including images of live specimens. However, in my copy there are some misprints; e.g. on p. 110 with only three images shown in Fig. 6 which is supposed to show ten. Also Fig. 13 has a misprint, showing only two of the supposedly 12 images, among which unfortunately also the figures of the new species.
And I suspect that the (damaged) specimen identified as Naesiotus sp. is in fact a Protoglyptus species; they share the same type of protoconch sculpture and so the confusion is understandable.

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Update: Luiz Simone, one of the authors, kindly send me a copy in which all images were present. Seemingly the transfer originally affected only SEM photos. The new species is now figured in Fig. 13 I-L.

Reference:
Salvador, R.B. et al., 2018. Terrestrial gastropods from Pedra Talhada Biological Reserve, Alagoas state, Brazil, with the description of a new species of Radiodiscus (Gastropoda: Charopidae). – Archiv für Molluskenkunde, 147 (1): 101-128.