Developments in avian cytotaxonomy: implications for Afro-avian Species

Abstract

Ejere. VC. 2000. Developments in avian cytotaxonomy: implications for Afro-avian Species. Ostrich 71 (1 & 2): 40.

Karyological studies of the extant species of birds have progressed slower than those of other animal groups. To date, a paltry proportion of less than 20% of about an estimated 9 000 avian species have been karyotyped, such that for most orders, karyological information remains largely scanty. Data accumulated so far, has revealed a lot of interesting features of the typical avian karyotype. Essentially, the karyotype is dichotomous, containing several pairs of fairly big chromosomes (= macrochomosomes) and very small to minute chromosome elements (= microchromosmes). The diploid chromosome number is also variable, ranging from 2n = 40 to 2n = 92 with a mode of 2n = 80 chromosomes observed in a majority of species. Studies have further revealed that chromosomal evolution in birds is highly conservative especially with reference to the first 3 pairs of macrochromosomes. (Group A), while considerable variability in number and morphology occurs in the remaining groups of chromosome elements. These variabilities, as well as the homologies revealed by chromosome banding techniques, have aided the cytotaxonomy of various individual avian groups. In this review, the karyological as well as the phylogenetic relationships of the various avian species so far karyotyped, vis-a-vis the cytotaxonomic implications for the abundant Afro-avian fauna are highlighted. Similarly, the significance of the observed peculiarities in the avian karyotype is briefly discussed. Suggestions are proffered in respect of the application of karyotype analysis technique to bird conservation in Africa. This will focus mainly on the identification of the gender of birds for the singular purpose of breeding rare and endangered species for zoological gardens and related institutions.