Evolutionary modification of T-brain (tbr) expression patterns in sand dollar

The sand dollars are a group of irregular echinoids that diverged from other regular sea urchins approximately 200 million years ago. We isolated two orthologs of T-brain (tbr), Smtbr and Pjtbr, from the indirect developing sand dollar Scaphechinus mirabilis and the direct developing sand dollar Peronella japonica, respectively. The expression patterns of Smtbr and Pjtbr during early development were examined by whole mount in situ hybridization. The expression of Smtbr was first detected in micromere descendants in early blastula stage, similar to tbr expression in regular sea urchins. However, unlike in regular sea urchin, Smtbr expression in middle blastula stage was detected in micromere-descendent cells and a subset of macromere-descendant cells. At gastrula stage, expression of Smtbr was detected in part of the archenteron as well as primary mesenchyme cells. A similar pattern of tbr expression was observed in early Peronella embryos. A comparison of tbr expression patterns between sand dollars and other echinoderm species suggested that broader expression in the endomesoderm is an ancestral character of echinoderms. In addition to the endomesoderm, Pjtbr expression was detected in the apical organ, the animal-most part of the ectoderm.     

Cladistic analysis of cassiduloid echinoids: trying to see the phylogeny for the trees

Using DNA fingerprinting we estimated the reproductive success of 49 adult birds belonging to 16 breeding groups of the sexually monomorphic brown skua (Calharacta lonnbergi) from the Chatham Islands (New Zealand). This population has a variable mating system, breeding in both monogamous and polyandrous groups. The parentage of 45 chicks produced over three breeding seasons was unequivocally determined using the multilocus probes 33.15 and 33.6. We found no evidence of either extra-pair or extra-group fertilization and there was no evidence to suggest egg dumping by females in any breeding group. Consequently, in the case of pairs, parentage of all chicks was assigned to the resident adult birds. In addition, band sharing analysis indicated that members of communal groups were not close relatives. In the 10 communally breeding groups examined, multiple paternity within a clutch was recorded on two of the 12 occasions in which two chicks were reared. Analysis of the parentage of offspring belonging to different groups, from different years, demonstrated that the number of chicks produced by some adult males varied considerably between seasons. In contrast, the reproductive success of other individuals was constant; for example, one male produced two chicks in each of the three seasons it was studied, while other males in communal groups did not produce any chicks during the course of this study. Fitness is a lifetime parameter, and any assessment of it requires studies over at least the average lifetime of an individual. The findings presented in this study suggest that, for brown skuas, there are significant differences in the reproductive success of some adult males in different breeding seasons. These results indicate that estimates of reproductive fitness based on only a single breeding season's data can be seriously inaccurate. Should temporal changes in paternity (and/or maternity) be shown to be common phenomena in other species, then such results would have major implications for the interpretation of parentage studies.     

Gladistic analysis of the living cassiduloids (Echinoidea), and the effects of character ordering and successive approximations weighting

The crown group of the Neognathostomata, one of the three major clades of irregular echinoids, comprises the paraphyletic order Cassiduloida, the family Neolampadidae, and the order Clypeasteroida. Recent studies have recognized the latter two groups as sister taxa, while suggesting different relationships with other cassiduloids. Here parsimony analyses of 57 qualitative morphologic characters (having 127 states) are employed to determine relationships among all 30 living cassiduloid species and three representative clypeasteroids. The 30 trees (of 144 steps) obtained using unordered multistate characters support the branching sequence: apatopygids (Apatopygus and Porterpygus) , echinolampadids (Echinolampas and Conolampas) , cassidulids (Oligopodia, Eurkodia, Rhyncholampas and Cassidulus), Studeria , neolampadids and clypeasteroids. Contrary to claims in the literature, ordering multistate characters does not improve resolution, although the majority-rule consensus of the resulting 84 trees supports the same relationships among genera. Trees found using only characters likely to be preserved in fossils differ only in the arrangement of the neolampadid taxa. Successive approximations weightings are found to be sensitive to arbitrary choices of the scaling factor and truncation. Weightings can lead to increases or decreases in the number of most parsimonious trees and the congruence among trees.