Evolution of body shape in differently coloured sympatric congeners and allopatric populations of Lake Malawi's rock-dwelling cichlids

Comparative reproductive biology of two sympatric Hypostomus in a Neotropical river

Congeneric species often coexist in sympatry using behavioral and morphological adaptations to reduce competition and interspecific interference, but reproductive patterns behind coexistence remain unknown. We analyzed the gonadal morphology and development, reproductive cycle, and population structure of two sympatric congeneric fishes to evaluate the degree of overlap and differentiation of the reproductive biology between species in a Neotropical river. Development of testes and ovaries were similar between species, both showing asynchronous gonadal development, large diameter of gametes and synthesis of mucosubstances by follicle cells to form adhesive eggs. Although the morphometry of germ cells did not present differences, the zona radiata of mature eggs in Hypostomus garmani was markedly thicker than H. francisci, which suggests different spawning habitats. Both species have greater reproductive activity in the rainy season, concomitant with increase in water temperature, however H. garmani initiates and ends its reproduction earlier than H. francisci, indicating a differentiation of reproductive periods. Sexually mature males and females of H. francisci reproduced at a larger mean size then H. garmani. The two congeneric species had a similar abundance and sex ratios in the study area. Results show that although the species exhibited broad overlap of reproductive traits, a spatial and temporal differentiation of the reproductive biology was present. This study contributes to understanding reproductive mechanisms that may facilitate coexistence between congeneric sympatric species.

A phylogeny of the genus Limia (Teleostei: Poeciliidae) suggests a single-lake radiation nested in a Caribbean-wide allopatric speciation scenario

OBJECTIVE

The Caribbean is an important global biodiversity hotspot. Adaptive radiations there lead to many speciation events within a limited period and hence are particularly prominent biodiversity generators. A prime example are freshwater fish of the genus Limia, endemic to the Greater Antilles. Within Hispaniola, nine species have been described from a single isolated site, Lake Miragoâne, pointing towards extraordinary sympatric speciation. This study examines the evolutionary history of the Limia species in Lake Miragoâne, relative to their congeners throughout the Caribbean.

RESULTS

For 12 Limia species, we obtained almost complete sequences of the mitochondrial cytochrome b gene, a well-established marker for lower-level taxonomic relationships. We included sequences of six further Limia species from GenBank (total N  = 18 species). Our phylogenies are in concordance with other published phylogenies of Limia. There is strong support that the species found in Lake Miragoâne in Haiti are monophyletic, confirming a recent local radiation. Within Lake Miragoâne, speciation is likely extremely recent, leading to incomplete lineage sorting in the mtDNA. Future studies using multiple unlinked genetic markers are needed to disentangle the relationships within the Lake Miragoâne clade.

Beyond Pairwise Interactions: Multispecies Character Displacement in Mexican Freshwater Fish Communities

Competition has long been recognized as a central force in shaping evolution, particularly through character displacement. Yet research on character displacement is biased, as it has focused almost exclusively on pairs of interacting species while ignoring multispecies interactions. Communities are seldom so simple that only pairs of species interact, and it is not clear whether inferences from pairwise interactions are sufficient to explain patterns of phenotypes in nature. Here, we test for character displacement in a natural system of freshwater fishes in western Mexico that contains up to four congeneric species of the genus Poeciliopsis. We analyzed body shape differences between populations with different numbers of competitors while accounting for confounding environmental variables. Surprisingly, we found evidence for convergent character displacement in populations of P. prolifica, P. viriosa, and P. latidens. We also found that the convergence in body shape was not consistently in the same direction, meaning that when three or more competitors co-occurred, we did not find more extreme body shapes compared with when there were only two competitors. Instead, when three or more competitors co-occurred, body shape was intermediate between the shape found with a pair of species and the shape found with no competitor present. This intermediate shape suggests that evolution in multispecies communities likely occurs in response to several competitors rather than to simple pairwise interactions. Overall, our results suggest that competition among multiple species is more complex than simple pairwise competitive interactions.

Body shape differences in a pair of closely related Malawi cichlids and their hybrids: Effects of genetic variation, phenotypic plasticity, and transgressive segregation

Phenotypic differences may have genetic and plastic components. Here, we investigated the contributions of both for differences in body shape in two species of Lake Malawi cichlids using wild-caught specimens and a common garden experiment. We further hybridized the two species to investigate the mode of gene action influencing body shape differences and to examine the potential for transgressive segregation. We found that body shape differences between the two species observed in the field are maintained after more than 10 generations in a standardized environment. Nonetheless, both species experienced similar changes in the laboratory environment. Our hybrid cross experiment confirmed that substantial variation in body shape appears to be genetically determined. The data further suggest that the underlying mode of gene action is complex and cannot be explained by simple additive or additive-dominance models. Transgressive phenotypes were found in the hybrid generations, as hybrids occupied significantly more morphospace than both parentals combined. Further, the body shapes of transgressive individuals resemble the body shapes observed in other Lake Malawi rock-dwelling genera. Our findings indicate that body shape can respond to selection immediately, through plasticity, and over longer timescales through adaptation. In addition, our results suggest that hybridization may have played an important role in the diversification of Lake Malawi cichlids through creating new phenotypic variation.

Patterns of contact call differentiation in the panmictic East African Abyssinian White-eye Zosterops abyssinicus (Aves: Passeriformes)

Species distribution patterns range from highly disjunct to continuous, depending on their ecological demands and the availability of respective habitats. East African savannahs are mostly interconnected and ecologically comparatively homogenous and thus provide a prerequisite for a rather panmictic distribution pattern for species occurring in this habitat. The Abyssinian white-eye Zosterops abyssinicus is a savannah inhabiting bird species, representing such a continuous distribution. This species occurs in high abundances and is very mobile, and past population genetic studies have suggested that gene flow is high and genetic differentiation is low even across relatively large geographic distances. Further, only little morphological differences were found. In order to test for potential divergence in acoustic traits despite its interconnected geographic distribution, we analyzed 2795 contact calls of Z. abyssinicus, which were recorded at 19 sites across Kenya. Our data indicate weak, but significant differentiation in call characteristics across latitudinal gradients. We found strong changes in call characteristics in populations where Z. abyssinicus occurs in sympatry with its highland congener, Zosterops poliogaster. However, the changes in call characteristics in sympatry were in different directions and lead to strong differentiation of the sympatric populations to other conspecific populations potentially representing a case of cascade reinforcement. The detected spatial gradients likely result from ecological differences and balancing effects of natural and sexual selection.

Quantitative Genetic Analyses of Male Color Pattern and Female Mate Choice in a Pair of Cichlid Fishes of Lake Malawi, East Africa

The traits involved in sexual selection, such as male secondary sexual characteristics and female mate choice, often co-evolve which can promote population differentiation. However, the genetic architecture of these phenotypes can influence their evolvability and thereby affect the divergence of species. The extraordinary diversity of East African cichlid fishes is often attributed to strong sexual selection and thus this system provides an excellent model to test predictions regarding the genetic architecture of sexually selected traits that contribute to reproductive isolation. In particular, theory predicts that rapid speciation is facilitated when male sexual traits and female mating preferences are controlled by a limited number of linked genes. However, few studies have examined the genetic basis of male secondary sexual traits and female mating preferences in cichlids and none have investigated the genetic architecture of both jointly. In this study, we artificially hybridized a pair of behaviorally isolated cichlid fishes from Lake Malawi and quantified both melanistic color pattern and female mate choice. We investigated the genetic architecture of both phenotypes using quantitative genetic analyses. Our results suggest that 1) many non-additively acting genetic factors influence melanistic color patterns, 2) female mate choice may be controlled by a minimum of 1-2 non-additive genetic factors, and 3) F2 female mate choice is not influenced by male courting effort. Furthermore, a joint analysis of color pattern and female mate choice indicates that the genes underlying these two traits are unlikely to be physically linked. These results suggest that reproductive isolation may evolve rapidly owing to the few genetic factors underlying female mate choice. Hence, female mate choice likely played an important role in the unparalleled speciation of East African cichlid fish.