Life in the unthinking depths: energetic constraints on encephalization in marine fishes.

Several hypotheses have been proposed to explain the limitation of brain size in vertebrates. Here, we test three hypotheses of brain size evolution using marine teleost fishes: the direct metabolic constraints hypothesis (DMCH), the expensive tissue hypothesis and the temperature-dependent hypothesis. Our analyses indicate that there is a robust positive correlation between encephalization and basal metabolic rate (BMR) that spans the full range of depths occupied by teleosts from the epipelagic (< 200 m), mesopelagic (200-1000 m) and bathypelagic (> 4000 m). Our results disentangle the effects of temperature and metabolic rate on teleost brain size evolution, supporting the DMCH. Our results agree with previous findings that teleost brain size decreases with depth; however, we also recover a negative correlation between trophic level and encephalization within the mesopelagic zone, a result that runs counter to the expectations of the expensive tissue hypothesis. We hypothesize that mesopelagic fishes at lower trophic levels may be investing more in neural tissue related to the detection of small prey items in a low-light environment. We recommend that comparative encephalization studies control for BMR in addition to controlling for body size and phylogeny.

Convergence in trophic morphology and feeding performance among piscivorous natricine snakes.

Piscivory has independently evolved numerous times amongst snakes, and therefore these animals provide a powerful opportunity to test for convergent evolution in a vertebrate feeding system. In this study, we integrate performance trials with comparative methods to test the hypothesis that piscivory drives convergence in trophic morphology and feeding performance among natricine snakes. Within and across species, increasing the relative length of the quadrate bone in the skull is positively and strongly linked to a reduction in the time needed to swallow large fish prey. Thus, our feeding experiments suggest that a longer quadrate bone enables snakes to better conform their head shape to the shape of the prey during swallowing. Ancestral diet reconstructions and phylogenetically corrected multiple regression analyses further reveal that evolutionary increases in piscivory are coupled to the evolution of relatively longer quadrates, and hence improved feeding performance on fish prey in these animals. The exploitation of similar dietary niches drives the evolution of convergent trophic morphologies and feeding performances in natricine snakes.

Opening the black box: phylogenetics and morphological evolution of the Malagasy fossorial lizards of the subfamily "Scincinae".

The island of Madagascar harbors a highly endemic vertebrate fauna including a high diversity of lizards of the subfamily "Scincinae," with about 57 species in eight genera. Since limb reduction seems to have been a common phenomenon during the evolution of Malagasy "scincines," diagnosing evolutionary relationships based on morphology has been difficult. Phylogenetic analyses of multiple mitochondrial DNA sequences including the entire ND1, tRNA(LEU), tRNA(ILE), tRNA(GLN) genes, and fragments of the 12S and 16S rRNA and tRNA(MET) genes were conducted to test the monophyly of the largest genus Amphiglossus, and to evaluate the various formal and informal species groupings previously proposed for this species-rich group. A further objective was to determine the phylogenetic placements of the several greatly limb-reduced and limbless Malagasy "scincines" and ascertain whether any of these are derived from within the morphologically plesiomorphic Amphiglossus. As limb reduction in skinks is mostly associated with body elongation via an increase in the number of presacral vertebrae, we evaluate the pattern of evolution of the numbers of presacral vertebrae in the context of our phylogeny. We demonstrate that Amphiglossus as currently diagnosed is non-monophyletic, and the species fall into two major groups. One of these groups is a clade that contains the included species of the subgenus Amphiglossus (Madascincus) among other species and is a member of a larger clade containing Paracontias and Pseudoacontias. In the second group, the nominate subgenus Amphiglossus (Amphiglossus) forms several subclades within a larger clade that also contains Androngo crenni and Pygomeles braconnieri, and is sister to Voeltzkowia. All analyses provide strong support for the monophyly of Paracontias and Voeltzkowia. Based on the preferred phylogenetic hypothesis and weighted squared-change parsimony we show that the ancestor of the Malagasy clade was already elongated and had a moderately high number of presacral vertebrae (46-48), which is hypothesized to be the ancestral condition for the whole Malagasy "scincine" clade. We further demonstrate that both multiple increases and reductions of presacral vertebrae evolved in many clades of Malagasy "scincines" and that the use of presacral vertebrae as a major character to diagnose supraspecific units is dubious. Based on our results and published morphological evidence we consider Scelotes waterloti Angel, 1930 to be a junior synonym of Amphiglossus reticulatus (Kaudern, 1922).