Evolution of egg dummies in Tanganyikan cichlid fishes: the roles of parental care and sexual selection

Sexual selection has been suggested to be an important driver of speciation in cichlid fishes of the Great Lakes of Africa, and the presence of male egg dummies is proposed to have played a key role. Here, we investigate how mouthbrooding and egg dummies have evolved in Tanganyikan cichlids, the lineage which seeded the other African radiations, with a special emphasis on the egg dummies. Using modern phylogenetic comparative analyses and a phylogeny including 86% of the 200 described species, we provide formal evidence demonstrating correlated evolution between mouthbrooding and egg dummies in Tanganyikan cichlids. These results concur with existing evidence, suggesting that egg dummies have evolved through sensory exploitation. We also demonstrate that there is a strong evolutionary correlation between the presence of egg dummies and both pre‐ and post‐copulatory sexual selection. Moreover, egg dummy evolution was contingent on the intensity of pre‐ and post‐copulatory sexual selection in Tanganyikan cichlids. In sum, our results provide evidence supporting the hypothesis of egg dummies evolving through sensory exploitation and highlight the role of sexual selection in favouring the evolution and maintenance of this trait.     

The ghosts of Gondwana and Laurasia in modern liverwort distributions

Recent advances in phylogenetics and, in particular, molecular dating, indicate that transoceanic dispersal has played an important role in shaping plant and animal distributions, obscuring any effect of tectonic history. Taxonomic sampling in biogeographic studies is, however, systematically biased towards vertebrates and higher plants and the possibility remains that a much stronger signature of ancient vicariance might be evident among other organisms, particularly among basal land plants. Here, an explicit Bayesian model‐based approach was used to investigate global‐scale biogeographic patterns among liverwort genera and to determine whether the patterns identified are consistent with the expectations of vicariance or dispersal scenarios. The distribution of each genus was mapped onto the phylograms describing the floristic affinities among areas in order to define the synapomorphic transitions supporting the observed groupings. The probabilities of change in a branch were calculated by implementing the Markov model of BayesTraits. The consistent ambiguity in ancestral state reconstructions returned by the unconstrained, two‐rate model indicated that the overall signal in the data was weak, leading us to test the performance of competing, explicit models. The analyses resolved clades of geographic areas that are mostly consistent with the kingdoms traditionally identified for plants and animals, but with strikingly lower rates of endemism. The major split observed in the phylograms is into almost entirely Laurasian and Gondwanan clades. Other patterns recovered by the analyses, including Wallace's line and the South Atlantic Disjunction, have also traditionally been interpreted in terms of vicariance. These observations contrast with the idea that, in spore‐dispersed organisms like bryophytes and pteridophytes, dispersal obscures evidence of vicariance. However, some discrepancies between the liverwort trees and expectations from a continental drift scenario were observed, such as the sister‐group relationship of the Australian and New Zealand floras, which is supported by the co‐occurrence of many genera, often endemic to these two areas. Together with an interpretation of the results within a phylogenetic context, our analyses suggest that patterns, which are at first sight consistent with an ancient vicariance hypothesis, may, in fact, conceal a complex mixture of relictual distributions and more recent, asymmetrical dispersal events. Our results provide a framework for testing specific evolutionary hypotheses concerning the extremely low levels of endemism in bryophytes and in particular, the significance of dispersal and cryptic diversification.     

Phylogenetic signal,feeding behaviour and brain volume in Neotropical bats

Comparative correlational studies of brain size and ecological traits (e.g. feeding habits and habitat complexity) have increased our knowledge about the selective pressures on brain evolution. Studies conducted in bats as a model system assume that shared evolutionary history has a maximum effect on the traits. However, this effect has not been quantified. In addition, the effect of levels of diet specialization on brain size remains unclear. We examined the role of diet on the evolution of brain size in Mormoopidae and Phyllostomidae using two comparative methods. Body mass explained 89% of the variance in brain volume. The effect of feeding behaviour (either characterized as feeding habits, as levels of specialization on a type of item or as handling behaviour) on brain volume was also significant albeit not consistent after controlling for body mass and the strength of the phylogenetic signal (λ). Although the strength of the phylogenetic signal of brain volume and body mass was high when tested individually, λ values in phylogenetic generalized least squares models were significantly different from 1. This suggests that phylogenetic independent contrasts models are not always the best approach for the study of ecological correlates of brain size in New World bats.     

When did plants become important to leaf‐nosed bats? Diversification of feeding habits in the family Phyllostomidae

A great proportion of bats of the New World family Phyllostomidae feed on fruit, nectar and pollen, and many of them present adaptations to feed also on insects and small vertebrates. So far, attempts to examine the diversification of feeding specialization in this group, and particularly the evolution of nectarivory and frugivory, have provided contradictory results. Here we propose a molecular phylogenetic hypothesis for phyllostomids. On the basis of a matrix of feeding habits that takes into account geographical and seasonal variation, we tested different hypotheses of the evolution of feeding specializations in the group. We find strong support for the evolutionary model of a direct dietary diversification from insectivory. The estimates of divergence times of phyllostomid bats and the reconstruction of ancestral states with a Bayesian approach support the parallel evolution of frugivory in five lineages and of nectarivory in three lineages during the Miocene. On the basis of these findings, and recent dietary studies, we propose that during the evolution of phyllostomids switches to new feeding mechanisms to access to abundant and/or underexploited resources provided selective advantages that favoured the appearance of ecological innovations independently in different lineages of the family. We did not find evidences to support or reject the hypothesis that the insectivorous most recent common ancestor of all phyllostomids was also phytophagous.     

Structure,development, and evolutive patterns of spermatozoa in rhabditid nematodes (Nematoda: Rhabditida)

Spermatogenesis of five rhabditid nematodes was studied using transmission electron microscopy and is described herein. Structure and development of nematode sperm in all available representatives of the extensive order Rhabditida have been analysed and the main characteristics of each infraorder are discussed. The ancestral sperm of the order Rhabditida was reconstructed using maximum likelihood and Bayesian methods based on 44 ultrastructural sperm characters. The hypothetical ancestral spermatogenesis of the order Rhabditida agrees with the previously suggested “rhabditid” pattern and appears to be conserved throughout the order Rhabditida. Despite the enormous variation of rhabditid nematodes, few groups deviate from the ancestral pattern. This conserved pattern can be informative within the phylum Nematoda at order level, but poses limitations when used in taxonomic and phylogenetic analysis within Rhabditida.     

Sexual selection determines parental care patterns in cichlid fishes

Despite a massive research effort, our understanding of why, in most vertebrates, males compete for mates and females care for offspring remains incomplete. Two alternative hypotheses have been proposed to explain the direction of causality between parental care and sexual selection. Traditionally, sexual selection has been explained as a consequence of relative parental investment, where the sex investing less will compete for the sex investing more. However, a more recent model suggests that parental care patterns result from sexual selection acting on one sex favoring mating competition and lower parental investment. Using species-level comparative analyses on Tanganyikan cichlid fishes we tested these alternative hypotheses employing a proxy of sexual selection based on mating system, sexual dichromatism, and dimorphism data. First, while controlling for female reproductive investment, we found that species with intense sexual selection were associated with female-only care whereas species with moderate sexual selection were associated with biparental care. Second, using contingency analyses, we found that, contrary to the traditional view, evolutionary changes in parental care type are dependent on the intensity of sexual selection. Hence, our results support the hypothesis that sexual selection determines parental care patterns in Tanganyikan cichlid fishes.