A study of incipient speciation between Drosophila albomicans and D. nasuta Open Access

Woldesellassie, Fitsum Negussie (2011)

Permanent URL: https://etd.library.emory.edu/concern/etds/02870w387?locale=en
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Abstract

Abstract
A study of incipient speciation between Drosophila albomicans and D. nasuta
By Fitsum Woldesellassie
Two fruit fly species, Drosophila nasuta and D. albomicans, are closely related incipient species. These two species have allopatric distribution and are morphologically indistinguishable. Past studies reported inconsistent results on their pre-zygotic isolation but little data on their post-zygotic isolation. Notably, sex-ratio meiotic drive was observed in the F1 male from Okinawan D. albomicans female crossed to Indian D. nasuta male‚ but not from the reciprocal cross. Fertile hybrids and perpetual hybrid population can be easily made between these two species in lab, thus questioning their status as separate species. Here, I address the issue of speciation status by assessing the pre-mating and post-zygotic isolations between D. albomicans and D. nasuta. We assayed the courtship behavior by direct observation and the mating frequency by multiple choice test. The courtship behavior between these two species did not differ from that within species, and the mating frequency was also similar between and within species. Overall, there is none or at best very weak pre-mating isolation between these two species. Through a novel test protocol that allows us to accurately quantify sperm production, we compared fertility among F1 males from both reciprocal crosses within species and between species. The F1 male from Okinawan D. albomicans female x Indian D. nasuta male‚ produced very few sperm, just about 5% of that by the reciprocal male, who produced significantly more sperm than the intraspecific control. We also found gross abnormality in spermatogenesis accompanying sperm reduction. The concurrence of sex-ratio meiotic drive and hybrid male sterility suggests a possible causal link in between, consistent with the theory that genomic conflict in general, sex-ratio meiotic drive in particular, is a predominant evolutionary force in speciation.

Table of Contents

Table of Contents


Introduction ...................................................................1
Materials and Methods .....................................................5
Result ..........................................................................12
Discussion ....................................................................15
References ...................................................................20


Tables and Figures

Figure legends ..............................................................24
Figure 1 ......................................................................26
Figure 2 ......................................................................27
Figure 3 ......................................................................28
Figure 4 ......................................................................29
Figure 5 ......................................................................30
Figure 6 ......................................................................31
Figure 7 ......................................................................32
Table 1 .......................................................................33

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