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Revealing the mechanisms of sexual isolation in a case of sympatric and parallel ecological divergence

Conde-Padín, Paula; Cruz, Raquel; Hollander, Johan LU and Rolán-Alvarez, Emilio (2008) In Biological Journal of the Linnean Society 94(3). p.513-526
Abstract
Two ecotypes of a marine intertidal snail (Littorina saxatilis), living at different microhabitats and shore levels, have evolved in sympatry and in parallel across the Galician rocky shore. These ecotypes differ in many traits (including size) due to differential adaptation. They meet, mate assortatively, and partially hybridize at the mid shore where the two microhabitats overlap. The partial sexual isolation observed is claimed to be a side-effect of the size differences between ecotypes combined with a size assortative mating found in most populations of this species. We investigated this hypothesis using three complementary experimental approaches. First, we investigated which of the different shell variables contributed most to the... (More)
Two ecotypes of a marine intertidal snail (Littorina saxatilis), living at different microhabitats and shore levels, have evolved in sympatry and in parallel across the Galician rocky shore. These ecotypes differ in many traits (including size) due to differential adaptation. They meet, mate assortatively, and partially hybridize at the mid shore where the two microhabitats overlap. The partial sexual isolation observed is claimed to be a side-effect of the size differences between ecotypes combined with a size assortative mating found in most populations of this species. We investigated this hypothesis using three complementary experimental approaches. First, we investigated which of the different shell variables contributed most to the variation in individual sexual isolation in the field by using two new statistics developed for that purpose: (1) pair sexual isolation and (2) ri, which is based on the Pearson correlation coefficient. We found that size is the most important trait explaining the sexual isolation and, in particular, the males appear to be the key sex contributing to sexual isolation. Second, we compared the size assortative mating between regions: exposed rocky shore populations from north-westwern Spain (showing incomplete reproductive isolation due to size assortative mating) and protected Spanish and Swedish populations (showing size assortative mating but not reproductive isolation between ecomorphs). Most of the variation in size assortative mating between localities was significantly explained by the within-population level of variation on size. Third, we performed a laboratory male choice experiment, which further suggested that the choice is made predominantly on the basis of size. These results confirm the mechanism proposed to explain the sexual isolation in the Galician hybrid zone and thus support this case as a putative example of parallel incipient speciation. (Less)
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author
organization
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Contribution to journal
publication status
published
subject
keywords
assortative mating, hybrid zone, incipient speciation, Littorina saxatilis, mate choice, mating behaviour, mate discrimination
in
Biological Journal of the Linnean Society
volume
94
issue
3
pages
513 - 526
publisher
Linnean Society of London
external identifiers
  • scopus:45249121204
ISSN
0024-4066
DOI
10.1111/j.1095-8312.2008.00998.x
language
English
LU publication?
yes
id
0d780bcc-af48-4f01-9ed6-6465c4f606ee (old id 1982104)
date added to LUP
2011-08-19 13:02:33
date last changed
2017-07-30 03:53:27
@article{0d780bcc-af48-4f01-9ed6-6465c4f606ee,
  abstract     = {Two ecotypes of a marine intertidal snail (Littorina saxatilis), living at different microhabitats and shore levels, have evolved in sympatry and in parallel across the Galician rocky shore. These ecotypes differ in many traits (including size) due to differential adaptation. They meet, mate assortatively, and partially hybridize at the mid shore where the two microhabitats overlap. The partial sexual isolation observed is claimed to be a side-effect of the size differences between ecotypes combined with a size assortative mating found in most populations of this species. We investigated this hypothesis using three complementary experimental approaches. First, we investigated which of the different shell variables contributed most to the variation in individual sexual isolation in the field by using two new statistics developed for that purpose: (1) pair sexual isolation and (2) ri, which is based on the Pearson correlation coefficient. We found that size is the most important trait explaining the sexual isolation and, in particular, the males appear to be the key sex contributing to sexual isolation. Second, we compared the size assortative mating between regions: exposed rocky shore populations from north-westwern Spain (showing incomplete reproductive isolation due to size assortative mating) and protected Spanish and Swedish populations (showing size assortative mating but not reproductive isolation between ecomorphs). Most of the variation in size assortative mating between localities was significantly explained by the within-population level of variation on size. Third, we performed a laboratory male choice experiment, which further suggested that the choice is made predominantly on the basis of size. These results confirm the mechanism proposed to explain the sexual isolation in the Galician hybrid zone and thus support this case as a putative example of parallel incipient speciation.},
  author       = {Conde-Padín, Paula and Cruz, Raquel and Hollander, Johan and Rolán-Alvarez, Emilio},
  issn         = {0024-4066},
  keyword      = {assortative mating,hybrid zone,incipient speciation,Littorina saxatilis,mate choice,mating behaviour,mate discrimination},
  language     = {eng},
  number       = {3},
  pages        = {513--526},
  publisher    = {Linnean Society of London},
  series       = {Biological Journal of the Linnean Society},
  title        = {Revealing the mechanisms of sexual isolation in a case of sympatric and parallel ecological divergence},
  url          = {http://dx.doi.org/10.1111/j.1095-8312.2008.00998.x},
  volume       = {94},
  year         = {2008},
}