Intron “sliding” and the diversity of intron positions

Alignments of homologous genes typically reveal a great diversity of intron locations, far more than could fit comfortably in a single gene. Thus, a minority of these intron positions could be inherited from a single ancestral gene, but the larger share must be attributed to subsequent events of intron gain or intron “sliding” (movement from one position to another within a gene). Intron sliding has been argued from cases of discordant introns and from putative spatial clustering of intron positions. A list of 32 cases of discordant introns is presented here. Most of these cases are found to be artefactual. The spatial and phylogenetic distributions of intron positions from five published compilations of gene data, comprising 205 intron positions, have been examined systematically for evidence of intron sliding. The results suggest that sliding, if it occurs at all, has contributed little to the diversity of intron positions.

Parasite abundance and diversity in mammals: correlates with host ecology.

Fecally dispersed parasites of 12 wild mammal species in Mudumalai Sanctuary, southern India, were studied. Fecal propagule densities and parasite diversity measures were correlated with host ecological variables. Host species with higher predatory pressure had lower parasite loads and parasite diversity. Host body weight, home range, population density, gregariousness, and diet did not show predicted effects on parasite loads. Measures of alpha diversity were positively correlated with parasite abundance and were negatively correlated with beta diversity. Based on these data, hypotheses regarding determinants of parasite community are discussed.