Ecological differentiation of natural populations of Drosophila melanogaster, Drosophila simulans, and another drosophilid, Zaprionus tuberculatus, in ''Evolution Canyon,'' Mount Carmel, Israel, is well established. The fitness complex of D. melanogaster includes oviposition temperature preferences, tolerance to high temperature, drought stress and starvation, and different longevity patterns. This remarkable differentiation has evolved despite small interslope distances (only 100 -400 m), within easy dispersal distance. The differences between populations are those expected from genetic adaptation to local microclimates. How such differentiation could evolve and be maintained despite the likelihood of genetic exchange between populations is a challenging question. We hypothesized that interslope microclimatic differences caused strong differential selection for stress tolerance, accompanied by behavioral differentiation (habitat choice and reduced migration rate), reinforced by sexual isolation. Here we report highly significant mate choice by flies from different slopes of the canyon, with preference for sexual partners originating from the same slope. No preferences were found when the sexual partners belonged to different isofemale lines from the same slope.T he origin of reproductive isolation is the central event in the evolution of biological species (1, 2). Sexual isolation may evolve either in allopatry or sympatry, with and without geographical separation, respectively. It is widely accepted that postmating (postzygotic) isolation results from and completes the evolutionary divergence, whereas premating (prezygotic) isolation is associated with its initial stages (refs. 3-5 and references therein). The selectionist paradigm explains both allopatric and sympatric premating isolation as a result of divergent selection. However, the proposed versions of this selection-induced process vary significantly, especially with respect to sympatry. The main problem of sympatric speciation can be formulated as follows (3,(6)(7)(8)(9)(10). Is sexual isolation an incidental by-product of genetic divergence? Or, alternatively, is it selected directly because of its contribution to higher fitness?No clear answers to these questions are yet available. We are still far from understanding how isolation evolves, mainly because of scarcity of evidence, especially in the sympatric scenario. Understanding how selection works, quantifying its effects, and characterizing its interaction with other factors contributing to the differentiation of natural populations (migration, habitat choice, sexual behavior, etc.) are among the major issues of evolutionary biology. A wide range of genetic organization patterns, from major genes and compact blocks of epistatic (coadapted) genes to multiple loci dispersed over many chromosomes, was revealed in laboratory studies (refs. 11-13; for review, see also ref. 14). Much less is known about the population-genetic basis of adaptation and speciation in nature, despite an abundance of field ...
The strong microscale interslope environmental di¡erences in`Evolution Canyon' provide an excellent natural model for sympatric speciation. Our previous studies revealed signi¢cant slope-speci¢c di¡er-ences for a ¢tness complex of Drosophila. This complex involved either adaptation traits (tolerance to high temperature, di¡erent viability and longevity pattern) or behavioural di¡erentiation, manifested in habitat choice and non-random mating. This remarkable di¡erentiation has evolved despite a very small interslope distance (a few hundred metres only). Our hypothesis is that strong interslope microclimatic contrast caused di¡erential selection for ¢tness-related traits accompanied by behavioural di¡erentiation and reinforced by some sexual isolation, which started incipient speciation. Here we describe the results of a systematic analysis of sexual behaviour in a non-choice situation and several reproductive parameters of D. melanogaster populations from the opposite slopes of`Evolution Canyon'. The evidence indicates that: (i) mate choice derives from di¡erences in mating propensity and discrimination; (ii) females from the milder north-facing slope discriminate strongly against males of the opposite slope; (iii) both sexes of the south-facing slope display distinct reproductive and behavioural patterns with females showing increased fecundity, shorter time before remating and relatively higher receptivity, and males showing higher mating propensity. These patterns represent adaptive life strategies contributing to higher ¢tness.
The genetic basis of population divergence leading to adaptive radiation and speciation is a major unresolved problem of evolutionary biology. Molecular elucidation of ''speciation genes'' advanced recently, yet it remains without clear identification of the gene complexes participating in reproductive isolation between natural populations, particularly, in sympatry. Genetic divergence was discovered between Drosophila melanogaster populations inhabiting ecologically contrasting, opposite slopes in ''Evolution Canyon'' (EC), Mt. Carmel, Israel. Interslope migration of flies is easy and verified. Nevertheless, significant interslope D. melanogaster population divergence was established at EC involving habitat choice, mate choice, thermal and drought tolerances, adaptive genes, and mobile elements. Parallel patterns of stress tolerance, habitat choice, and mate choice were demonstrated in Drosophila simulans at EC, although on a smaller scale. However, some tests for interslope genetic differentiation in Drosophila, derived from the opposite EC slopes, gave somewhat controversial results. Here we present new empirical data on interslope genetic divergence of Drosophila at EC, and summarize previous supporting and controversial results. We suggest that Drosophila populations at EC represent a rare example, demonstrating how selection overrides migration, and propose an ad hoc ecological model of incipient sympatric divergence.genetic divergence ͉ incipient differentiation ͉ natural populations ͉ sympatric evolution
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.