Non-reef environments impact the diversification of extant jacks, remoras and allies (Carangoidei, Percomorpha)

Various factors may impact the processes of diversification of a clade. In the marine realm, it has been shown that coral reef environments have promoted diversification in various fish groups. With the exception of requiem sharks, all the groups showing a higher level of diversity in reefs than in non-reef habitats have diets based predominantly on plankton, algae or benthic invert- ebrates. Here we explore the pattern of diversification of carangoid fishes, a clade that includes numerous piscivorous species (e.g. trevallies, jacks and dolphinfishes), using time-calibrated phylogenies as well as ecological and morphological data from both extant and fossil species. The study of caran- goid morphospace suggests that reef environments played a role in their early radiation during the Eocene. However, contrary to the hypothesis of a reef-association-promoting effect, we show that habitat shifts to non-reef environments have increased the rates of morphological diversification (i.e. size and body shape) in extant carangoids. Piscivory did not have a major impact on the tempo of diversification of this group. Through the ecological radiation of carangoid fishes, we demonstrate that non-reef environments may sustain and promote processes of diversification of different marine fish groups, at least those including a large proportion of piscivorous species

Can we detect adaptive radiations in marine fishes?

peer reviewedThe concept of adaptive radiation, according to which a biological lineage undergoes elevated rates of species diversification while at the same time experiencing divergence along ecological axis, is often invoked in evolutionary studies to explain the astonishing diversity of groups such as the cichlids of the African rift lakes, silverswords plants and honeycreeper birds in Hawaii, and anole lizards in the Neotropics. Recent surveys of the scientific literature, however, revealed that most studies of adaptive radiation do not recover the expected signal of early burst of lineage diversification, and in several animal groups rates of cladogenesis and phenotypic evolution may often be unlinked, thus creating complex patterns in the tempo of lineage and trait diversification. Furthermore, in spite of the dramatic increase in number of studies of the tempo and mode of evolution in marine fishes during the past decade, very little evidence has been uncovered to support the idea that adaptive radiations played a role in generating their staggering diversity, and even when a signal of radiation is recovered this virtually never conforms to the “traditional” early burst scenario. Using examples from our research on diverse groups of marine teleost fishes such as jacks and allies (Carangoidei), pufferfish and allies (Tetraodontiformes) and snappers (Lutjanidae), we will discuss why it is so difficult to recover a signal of adaptive radiation in general, and early burst in particular, and offer some suggestions on how to test for these patterns

Changes in glucocorticoid receptor immunoreactivity after adrenalectomy and corticosterone treatment in the rat testis

The distribution of glucocorticoid receptor (GR) in the rat testis was investigated by means of immunocytochemistry (IR) and computer-assisted image analysis. A monoclonal antibody against rat liver GR showed the presence of GR IR selectively in the nuclei of interstitial and tubular cells. The semiquantitative microdensitometry of GR IR revealed that 77% of the specific staining was localized in the tubular compartment of rat testis. After adrenalectomy, GR IR was greatly reduced both in interstitial and tubular cells, roughly at the same degree. Corticosterone treatment (50 mg/kg, for 5 d) of adrenalectomized animals yielded a recovery of nuclear immunopositivity without changing the cellular distribution of GR, as observed in control rats. Nevertheless, the high dose of corticosterone administered produced a significant (p<0.01) decrease of GR IR with respect to control rats. These results provide evidence for a prevalent nuclear binding of GR in the tubular compartment in basal conditions. On the other hand, adrenalectomy or repeated corticosterone treatment seem to affect GR similarly in all positive cells without changing significantly the proportion of GR IR in the different testicular compartments. This uneven distribution of GR IR suggests that tubular cells can be a major target of corticosterone when affecting directly testicular functions in the rat