A study of incipient speciation between Drosophila albomicans and D. nasuta Public
Woldesellassie, Fitsum Negussie (2011)
Published
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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