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11.
Allopatric speciation often yields ecologically equivalent sister species, so that their
secondary admixis enforces competition. The shores of Lake Tanganyika harbor about 120
distinct populations of the cichlid genus Tropheus, but only some are sympatric.
When alone, Tropheus occupies a relatively broad depth zone, but in sympatry,
fish segregate by depth. To assess the effects of competition, we studied the partial
co-occurrence of Tropheus moorii ‘Kaiser'' and
‘Kirschfleck'' with Tropheus polli. A previous study demonstrated via
standardized breeding experiments that some observed differences between Tropheus
‘Kaiser'' living alone and in sympatry with T. polli have a genetic
basis despite large-scale phenotypic plasticity. Using geometric morphometrics and neutral
genetic markers, we now investigated whether sympatric populations differ consistently in
body shape from populations living alone and if the differences are adaptive. We found
significant differences in mean shape between non-sympatric and sympatric populations,
whereas all sympatric populations of both color morphs clustered together in shape space.
Sympatric populations had a relatively smaller head, smaller eyes and a more anterior
insertion of the pectoral fin than non-sympatric populations. Genetically, however,
non-sympatric and sympatric ‘Kaiser'' populations clustered together to the
exclusion of ‘Kirschfleck''. Genetic distances, but not morphological
distances, were correlated with geographic distances. Within- and between-population
covariance matrices for T. moorii populations deviated from proportionality. It
is thus likely that natural selection acts on both phenotypic plasticity and heritable
traits and that both factors contribute to the observed shape differences. The consistency
of the pattern in five populations suggests ecological character displacement. 相似文献
12.
Mating behaviour affects reproductive isolation and phenotypic differentiation. In Lake Tanganyika, the cichlid fish Tropheus moorii diversified into numerous, currently allopatric colour variants. Allopatric isolation is periodically interrupted by dispersal and secondary contact during lake level fluctuations, making long‐term differentiation partly dependent on assortative mating. Laboratory experiments with two moderately distinct morphs revealed assortative female preferences in one (Nakaku), but random mate choice in the other morph (Mbita). No discrimination was apparent between two subtly differentiated morphs (Chimba and Moliro). Tested against each other in a previous study, the highly distinct Moliro and Nakaku exhibited strong assortative preferences. The correlation between colour pattern similarity and mate discrimination suggests that allopatry and philopatric behaviour are less crucial for the maintenance of differentiation between highly distinct morphs than for more similar morphs. Interestingly, the asymmetric isolation in one pair of morphs is congruent with a pattern of unidirectional mitochondrial introgression between populations. 相似文献
13.
P. I. Hablützel M. P. M. Vanhove A. F. Grégoir B. Hellemans F. A. M. Volckaert J. A. M. Raeymaekers 《Journal of evolutionary biology》2014,27(10):2177-2190
Studying the genetic basis of host–parasite interactions represents an outstanding opportunity to observe eco‐evolutionary processes. Established candidates for such studies in vertebrates are immunogenes of the major histocompatibility complex (MHC). The MHC has been reported to reach high intra‐ and interindividual diversity, and a diverse MHC might be advantageous when facing infections from multiple parasites. However, other studies indicated that individuals with an intermediate number of MHC alleles are less infected with parasites or have other fitness advantages. In this study, we assessed the optimal number of MHC alleles in the blunt‐head cichlid Tropheus moorii from Lake Tanganyika. We investigated the influence of the interindividual variation in number of MHC length variants on parasite infection and body condition, measured by the amount of perivisceral fat reserves. Surprisingly, there was no correlation between parasite infection and number of MHC length variants or perivisceral fat deposits. However, the individual number of MHC length variants significantly correlated with the amount of perivisceral fat deposits in males, suggesting that male individuals with an intermediate number of alleles might be able to use their fat reserves more efficiently. 相似文献