Reproductive biology of the eastern shovelnose ray, Aptychotrema rostrata (Shaw & Nodder, 1794), from Moreton Bay, Queensland, Australia

The eastern shovelnose ray, Aptychotrema rostrata (Rhinobatidae), is an endemic batoid common to the east coast of Australia. The reproductive cycle was studied in Moreton Bay, south-eastern Queensland, over a 14-month period. Aptychotrema rostrata is an aplacental yolksac viviparous species with an annual, seasonal reproductive cycle in Moreton Bay. Females mature at 54-66 cm total length, and males at 60-68 cm total length. Gravid females were observed during September-November and parturition occurred in November-December. Vitellogenesis does not proceed in parallel with gestation. Ovulation and copulation probably occur during July-September, resulting in a gestational period of 3-5 months. Uterine fecundity ranges from 4 to 18, with a significant positive relationship between uterine fecundity and maternal body length. In mature males, a peak in the proportion of mature spermatocysts in the testes was observed in July, whereas gonadosomatic index peaked in April.

Interactions among endocrinology, seasonal reproductive cycles and the nesting biology of the female green sea turtle

We collected data on plasma levels of testosterone+5a-dihydrotestosterone (T+DHT) and corticosterone (CORT) from adult female green sea turtles (Chelonia mydas) from southern Queensland during distinct stages of their reproductive cycle. Those females capable of breeding in a given year had elevated plasma steroid levels (T+DHT 0.91 +/- 0.08; CORT 1.05 +/- 0.29 ng/ml), associated with follicular development, until courtship began in October. At the beginning of the nesting season in November plasma levels of 2 CORT were related to when the female first nested (r(2) = 0.06; F = 10.45; P = 0.01). However, they were not correlated with the number of clutches a female laid in that season (F = 3.65; P = 0.08). We repeatedly sampled 23 turtles over the nesting season and profiled changes in steroids immediately following oviposition of each clutch. Levels of T+DHT (range 0.41-0.58 ng/ml) and CORT (range 2.13-2.81 ng/ml) were similar through the early stages of the nesting season and inter-nesting period, and declined to near basal levels (T+DHT 0.37 +/- 0.03 and CORT 1.85 +/- ng/ml) following the last clutch for the season. Steroid hormone levels were also low (T+DHT 0.38 +/- 0.16; CORT 0.46 +/- 0.21 ng/ml) in four independent post-breeding (atretic) females; samples for these females were taken at a time when body condition was presumably at the lowest for the season. Subtle changes in the nesting environment, such as variation in nesting habitat or the time of night that nesting occurred, were associated with a small and slow CORT increase. We suggest CORT is increased in nesting females to assist in lipid transfer to prepare the ovarian follicles and/or the reproductive organs for ovulation.

GPI-anchored proteins are delivered to recycling endosomes via a distinct cdc42-regulated, clathrin-independent pinocytic pathway

Endocytosis of cell-surface proteins via specific pathways is critical for their function. We show that multiple glycosylphosphatidylinositol-anchored proteins (GPI-APs) are endocytosed to the recycling endosomal compartment but not to the Golgi via a nonclathrin, noncaveolae mediated pathway. GPI anchoring is a positive signal for internalization into rab5-independent tubular-vesicular endosomes also responsible for a major fraction of fluid-phase uptake; molecules merely lacking cytoplasmic extensions are not included. Unlike the internalization of detergent-resistant membrane (DRM)-associated interleukin 2 receptor, endocytosis of DRM-associated GPI-APs is unaffected by inhibition of RhoA or dynamin 2 activity. Inhibition of Rho family GTPase cdc42, but not Rac1, reduces fluid-phase uptake and redistributes GPI-APs to the clathrin-mediated pathway. These results describe a distinct constitutive pinocytic pathway, specifically regulated by cdc42.

Testing the link between the latitudinal gradient in species richness and rates of molecular evolution

Numerous hypotheses have been proposed to explain latitudinal gradients in species richness, but all are subject to ongoing debate. Here we examine Rohde's (1978, 1992) hypothesis, which proposes that climatic conditions at low latitudes lead to elevated rates of speciation. This hypothesis predicts that rates of molecular evolution should increase towards lower latitudes, but this prediction has never been tested. We discuss potential links between rates of molecular evolution and latitudinal diversity gradients, and present the first test of latitudinal variation in rates of molecular evolution. Using 45 phylogenetically independent, latitudinally separated pairs of bird species and higher taxa, we compare rates of evolution of two mitochondrial genes and DNA-DNA hybridization distances. We find no support for an effect of latitude on rate of molecular evolution. This result casts doubt on the generality of a key component of Rohde's hypothesis linking climate and speciation.

Direct visualization of Ras proteins in spatially distinct cell surface microdomains

Localization of signaling complexes to specific micro-domains coordinates signal transduction at the plasma membrane. Using immunogold electron microscopy of plasma membrane sheets coupled with spatial point pattern analysis, we have visualized morphologically featureless microdomains including lipid rafts, in situ and at high resolution. We find that an inner-plasma membrane lipid raft marker displays cholesterol-dependent clustering in microdomains with a mean diameter of 44 nm that occupy 35% of the cell surface. Cross-linking an outer-leaflet raft protein results in the redistribution of inner leaflet rafts, but they retain their modular structure. Analysis of Ras microlocalization shows that inactive H-ras is distributed between lipid rafts and a cholesterol-independent micro-domain. Conversely, activated H-ras and K-ras reside predominantly in nonoverlapping, cholesterol-independent microdomains. Galectin-1 stabilizes the association of activated H-ras with these nonraft microdomains, whereas K-ras clustering is supported by farnesylation, but not geranylgeranylation. These results illustrate that the inner plasma membrane comprises a complex mosaic of discrete microdomains. Differential spatial localization within this framework can likely account for the distinct signal outputs from the highly homologous Ras proteins.