Puzzles taxonomists have to solve
26-04-2008 10:29
Bostryx is the genus of South American land snails
that is really quite fascinating. There are several
hundreds of species (or at least: taxa) known and
these occur throughout the Andes with emphasis on
Peru. There is morphological variation is
astonishing, from turrited to discoidal and anything
in between.
While in 1979* I needed some 20 species to depict this variation, in the material collected by Weyrauch I found specimens from one locality covering nearly the whole range.
Imagine that the elongated shell in the right-hand upper corner gradually becomes the lower shell through a transitional series. That is not only taxonomically relevant to observe (found apart one would call these shells separate species), but raises a number of other questions as well. What is the genetical mechanism behind this phenomenon? Are there any ecological differences?
This is apparently the material to which Weyrauch referred in his 1956 paper*: "As I will illustrate in a later paper [which he never published], the variation in a population of a new subspecies of Bostryx eremothauma (Pilsbry) comprises all forms hitherto placed in the polyphyletic 'shape-types' of Peronaeus, Ataxus, Lissoacme, Platybostryx and Discobostryx [at the time that Weyrauch wrote this, these were all considered as subgenera of Bostryx; now synonyms of Bostryx sensu lato]. This great variation of shape, not observed in any other species of land shells, agress with the still greater diversification of shapes in different species of the genus Bostryx. This is evidently due to the young age of this genus". As I recently pointed out here, it is very well possible that in some places the speciation processes is in full progress. The Rio Rimac valley, where also the specimens were collected shown above, is definitely a place of special interest to any malacologist.
Incidentally, I came across a recent paper of Cook* mentioning that high-spired shells tend to be active on vertical surfaces, while low-spired species use horizontal substrates. Differences in shape are associated with microhabitats, which would suggest that the specimens shown here have different niches within the same locality. Unfortunately the museum labels don't tell us anything about it. For me it is one of the reasons why field work is a necessary complement to museum work and why it should be well documented.
References:
Breure, A.S.H. (1979) Systematics, phylogeny and zoogeography of Bulimulinae (Mollusca). Zoologische Verhandelingen 168: 1-215 [The variation in Bostryx is shown on p. 47].
Cook, L. M. (2008). Species richness in Madeiran land snails, and its causes. Journal of Biogeography 35, 647-653.
Weyrauch, W.K. (1956) The genus Naesiotus, with descriptions of new species and notes on other Peruvian Bulimulidae. Proceedings of the Academy of Natural Sciences of Philadelphia 108: 1-17.
While in 1979* I needed some 20 species to depict this variation, in the material collected by Weyrauch I found specimens from one locality covering nearly the whole range.
Imagine that the elongated shell in the right-hand upper corner gradually becomes the lower shell through a transitional series. That is not only taxonomically relevant to observe (found apart one would call these shells separate species), but raises a number of other questions as well. What is the genetical mechanism behind this phenomenon? Are there any ecological differences?
This is apparently the material to which Weyrauch referred in his 1956 paper*: "As I will illustrate in a later paper [which he never published], the variation in a population of a new subspecies of Bostryx eremothauma (Pilsbry) comprises all forms hitherto placed in the polyphyletic 'shape-types' of Peronaeus, Ataxus, Lissoacme, Platybostryx and Discobostryx [at the time that Weyrauch wrote this, these were all considered as subgenera of Bostryx; now synonyms of Bostryx sensu lato]. This great variation of shape, not observed in any other species of land shells, agress with the still greater diversification of shapes in different species of the genus Bostryx. This is evidently due to the young age of this genus". As I recently pointed out here, it is very well possible that in some places the speciation processes is in full progress. The Rio Rimac valley, where also the specimens were collected shown above, is definitely a place of special interest to any malacologist.
Incidentally, I came across a recent paper of Cook* mentioning that high-spired shells tend to be active on vertical surfaces, while low-spired species use horizontal substrates. Differences in shape are associated with microhabitats, which would suggest that the specimens shown here have different niches within the same locality. Unfortunately the museum labels don't tell us anything about it. For me it is one of the reasons why field work is a necessary complement to museum work and why it should be well documented.
References:
Breure, A.S.H. (1979) Systematics, phylogeny and zoogeography of Bulimulinae (Mollusca). Zoologische Verhandelingen 168: 1-215 [The variation in Bostryx is shown on p. 47].
Cook, L. M. (2008). Species richness in Madeiran land snails, and its causes. Journal of Biogeography 35, 647-653.
Weyrauch, W.K. (1956) The genus Naesiotus, with descriptions of new species and notes on other Peruvian Bulimulidae. Proceedings of the Academy of Natural Sciences of Philadelphia 108: 1-17.