Sexual dimorphism in an adaptive radiation: Does intersexual niche differentiation result in ecological character displacement?

Assessing brain neuroplasticity: Surface morphometric analysis of cortical changes induced by Quadrato motor training

Morphological markers for brain plasticity are still lacking and their findings are challenged by the extreme variability of cortical brain surface. Trying to overcome the "correspondence problem," we applied a landmark-free method (the generalized procrustes surface analysis (GPSA)) for investigating the shape variation of cortical surface in a group of 40 healthy volunteers (i.e., the practice group) subjected to daily motor training known as Quadrato motor training (QMT). QMT is a sensorimotor walking meditation that aims at balancing body, cognition, and emotion. More specifically, QMT requires coordination and attention and consists of moving in one of three possible directions on corners of a 50 × 50 cm2. Brain magnetic resonance images (MRIs) of practice group (acquired at baseline, as well as after 6 and 12 weeks of QMT), were 3D reconstructed and here compared with brain MRIs of six more volunteers never practicing the QMT (naïve group). Cortical regions mostly affected by morphological variations were visualized on a 3D average color-scaled brain surface indicating from higher (red) to lower (blue) levels of variation. Cortical regions interested in most of the shape variations were as follows: (1) the supplementary motor cortex; (2) the inferior frontal gyrus (pars opercolaris) and the anterior insula; (3) the visual cortex; (4) the inferior parietal lobule (supramarginal gyrus and angular gyrus). Our results show that surface morphometric analysis (i.e., GPSA) can be applied to assess brain neuroplasticity processes, such as those stimulated by QMT.

Can diet niche partitioning enhance sexual dimorphism?

Classic evolutionary theory suggests that sexual dimorphism evolves primarily via sexual and fecundity selection. However, theory and evidence are beginning to accumulate suggesting that resource competition can drive the evolution of sexual dimorphism, via ecological character displacement between sexes. A key prediction of this hypothesis is that the extent of ecological divergence between sexes will be associated with the extent of sexual dimorphism. As the stable isotope ratios of animal tissues provide a quantitative measure of various aspects of ecology, we carried out a meta-analysis examining associations between the extent of isotopic divergence between sexes and the extent of body size dimorphism. Our models demonstrate that large amounts of between-study variation in isotopic (ecological) divergence between sexes is nonrandom and may be associated with the traits of study subjects. We, therefore, completed meta-regressions to examine whether the extent of isotopic divergence between sexes is associated with the extent of sexual size dimorphism. We found modest but significantly positive associations across species between size dimorphism and ecological differences between sexes, that increased in strength when the ecological opportunity for dietary divergence between sexes was greatest. Our results, therefore, provide further evidence that ecologically mediated selection, not directly related to reproduction, can contribute to the evolution of sexual dimorphism.

Functional morphology of prey capture in stream-dwelling sailfin silversides (Telmatherinidae) based on high-speed video recordings

Understanding how ecology shapes the evolution of morphological traits is a major goal in organismal biology. By quantifying force of motion, hypotheses on the function of fundamental tasks of animals like feeding can be tested. Ray-finned fishes use various feeding strategies, classified into three main feeding modes: suction, ram and manipulation. While manipulation feeders are usually distinct in morphology and feeding behavior, differentiation between suction and ram feeders is often fine-scaled and transitional. Previous studies have identified different feeding modes and biomechanical adaptations on interspecific and intersexual levels in lake-dwelling sailfin silversides, species of a Sulawesi freshwater radiation. Functional feeding morphology of stream-dwelling species remained in contrast unstudied. We hypothesized that different requirements of riverine habitats favor the evolution of alternative functional adaptations in stream-dwelling sailfin silversides. To test this hypothesis, we investigated feeding of two phenotypically distinct riverine species, Telmatherina bonti and Marosatherina ladigesi, and their sexes, by high-speed videos and biomechanical models. The kinematic approaches identify T. bonti as ram feeder and M. ladigesi as suction feeder. Surprisingly, the biomechanical models of the jaw apparatus provide contradicting results: only one out of three studied parameters varies between both species. Contrarily to lake-dwelling Telmatherina, sexes of both species do not differ in feeding biomechanics. We conclude that T. bonti predominantly uses ram feeding while M. ladigesi primarily uses suction feeding as its main hunting strategy. Feeding biomechanics of stream-dwelling sailfin silversides are less distinct compared to lake-dwelling species, likely due to different trophic ecologies or less stable ecological conditions.