Mean FIS Research Articles

Population genetic evidence for species A, B, C and D of the Anopheles dirus complex in Thailand and enzyme electromorphs for their identification

Mixtures of chromosomal forms A, B, C and D in natural populations of Anopheles dirus Peyton & Harrison sensu lato in Thailand show significant positive values of Wright's fixation index for six enzyme-electromorph loci. The mean value of FIS over all loci was found to be +0.28 (SD 0.02), with a range of +0.57 (Odh) to +0.10 (Idh-2). Partitioning electromorph data for the chromosomal forms reduces the mean FIS to 0.03 (SD 0.01), which suggests that positive assortative mating is a characteristic of each form. This supports the hypothesis that the chromosomal/electrophoretic forms A, B, C and D represent four distinct biological species within the An. dirus complex. An example is given of the use of enzyme electromorphs as a means of vector identification during a malaria entomological field study involving a mixture of An. dirus species A and D. Electromorph identifications of 323 sp. A and 161 sp. D were more than 98% correct when cross-referenced to specific DNA probes.

Inbreeding in Natural Populations of the Annual Polyploid Fern Ceratopteris thalictroides (Parkeriaceae)

The degree of gametophytic selfing in natural populations was examined for the annual polyploid fern Ceratopteris thalictroides in several ways. Examination of sexual ontogeny of the gametophytes showed that two types of gametophytes were usually observed: large, cordate hermaphrodites with mature antheridia and archegonia and small, spatulate or amorphous males with numerous antheridia. The occurrence of the former may be correlated with gametophytic selfing, while that of the latter is indicative of the presence of antheridiogen, which can promote gametophytic crossing. Selfing potential was tested by growing isolated gametophytes. In this test, only 3 of 26 spore sources exhibited the presence of genetic load, and even the highest frequency of self-sterile gametophytes in these three was only 3.8%. These gametophytic results predicted a predominantly selfing mating system for this species. This prediction was tested using electropho- retic analysis of allozymes. Polymorphic band patterns were detected for IDH and PGI, and the genetic constitution of these variations was verified through progeny tests. Based on the frequencies of these allelically segregating variants, the rates of gametophytic selfing and F statistics were estimated for a population composed of five subpopulations. The estimated rates of gametophytic selfing were remarkably high, ranging from 0.600 to 1.000 with the mean FIS of 0.886. The estimated FST was 0.109 in IDH and 0.203 in PGI, values suggesting the occurrence of intrapopulational substructuring. The high level of gametophytic selfing in C. thalictroides is probably related to its polyploid nature and annually colonizing habit. An antheridiogen system may operate to compen- sate for the loss of genetic variability through predominant inbreeding.