Assortative Mating Preferences Research Articles

Assortative mating preferences between colour morphs of the endemic Lake Tanganyika cichlid genus Tropheus

Female mate preferences effectuate reproductive isolation among and sexual selection within species. Both mechanisms have been associated with the diversification and speciation of cichlid species flocks of the East African Great Lakes. In Lake Tanganyika, the endemic genus Tropheus has diversified into >100 geographic colour morphs. Although distributed allopatrically at present, water level fluctuations have repeatedly displaced and merged the benthic, rock-dwelling populations. Tests for assortative mating were performed to explore the potential for reproductive isolation between morphs in secondary contact, and to assess the importance of sexual selection for the diversification of this group. In contrast to other haplochromine cichlids, Tropheus is a sexually monochromatic, territorial and maternally mouthbrooding fish, which establishes temporary pair bonds prior to spawning. Female mate preference trials involved two-way choices between a homotypic and a heterotypic male and were conducted on allopatric populations of red and blue morphs from the southern part of Lake Tanganyika. Female affiliation time near each male’s compartment did not predict the mate preferences subsequently expressed in unrestrained interactions after removal of the compartment separators (spawning, pseudospawning and courtship). Consequently, mate preferences were inferred from unrestrained interactions with one test male at a time in replicate observation sessions. Of the 23 females tested, 13 courted, pseudospawned or spawned with the homotypic male, one blue female courted a red male, and nine females expressed no sexual motivation. The assortative mate preferences in the experiments (P < 0.01) suggest that colour differentiation between Tropheus populations can effectuate reproductive isolation, and is consistent with the notion that sexual selection contributed to the diversification of the genus.

Speciation and the evolution of dispersal along environmental gradients

We analyze the joint evolution of an ecological character and of dispersal distance in asexual and sexual populations inhabiting an environmental gradient. Several interesting phenomena resulting from the evolutionary interplay of these characters are revealed. First, asexual and sexual populations exhibit two analogous evolutionary regimes, in which either speciation in the ecological character occurs in conjunction with evolution of short-range dispersal, or dispersal distance remains high and speciation does not occur. Second, transitions between these two regimes qualitatively differ between asexual and sexual populations, with the former showing speciation with long-range dispersal and the latter showing no speciation with short-range dispersal. Third, a phenotypic gradient following the environmental gradient occurs only in the last case, i.e., for non-speciating sexual populations evolving towards short-range dispersal. Fourth, the transition between the evolutionary regimes of long-range dispersal with no speciation and short-range dispersal with speciation is typically abrupt, mediated by a positive feedback between incipient speciation and the evolution of short-range dispersal. Fifth, even though the model of sexual evolution analyzed here does not permit assortative mating preferences, speciation occurs for a surprisingly wide range of conditions. This illustrates that dispersal evolution is a powerful alternative to preference evolution in enabling spatially distributed sexual populations to respond to frequency-dependent disruptive selection.

Evaluating mate choice in the zebra finch

Finding reliable ways of assessing female mate choice is an essential prerequisite to understanding variation in female preferences and its impact on sexual selection. The zebra finch, Taeniopgyia guttata , is a classic avian model species for investigating mate choice and sexual selection, but to date virtually all work has been carried out using domesticated birds, and there are inconsistencies in the findings between studies. We tested three different methods for measuring female preferences in this species using both wild and domesticated birds. The first method was a traditional two-way mate choice chamber, where we measured the time spent with each male. The second method was a no-choice chamber where a single male and female were placed in the same cage for 5 min, such that the pair could physically interact, and the female's sexual response was recorded. The third method was an aviary set-up, comprising eight birds (four males and four females), and we recorded the number of pair-bonding behaviours observed over a 24-h period. In the aviary, we found that birds formed pair bonds almost exclusively with their own type (wild males paired with wild females, and domestic males paired with domestic females). In the two-way choice chamber, this assortative mating preference was only shown by domestic females, and in the no-choice test, only wild females showed this assortative mating preference. We discuss the possible reasons for these differences between mate choice tests and make recommendations for future studies on mate choice.

Early learning influences species assortative mating preferences in Lake Victoria cichlid fish

The Lake Victoria 'species flock' of cichlids is puzzling because reproductive isolation often occurs in the absence of substantial ecological differences among species. Theory predicts that this cannot evolve with most genetic mechanisms for mate choice. We provide the first evidence that learning, in the form of sexual imprinting, helps maintain reproductive isolation among closely related cichlid species. Using a cross-fostering experiment, we show that young females develop a sexual preference for males of their foster mothers' species, even reversing species assortative mating preferences. We suggest that learning creates favourable conditions for reproductive isolation to evolve.

Genetic isolation between two sympatric host plant races of the European corn borer, Ostrinia nubilalis Hübner. II: assortative mating and host-plant preferences for oviposition

The European corn borer, Ostrinia nubilalis Hubner, colonized maize (Zea mays L.) after its introduction into Europe about 500 years ago and is now considered one of the main pests of this crop. In northern France, two sympatric host races have been described: one feeding on maize and the other on mugwort (Artemisia vulgaris L.) and hop (Humulus lupulus L.). In a previous study, we showed that mating between the two races may be impeded by differences in the timing of moth emergence and in the composition of the sex pheromone produced by the females. In this study, we further investigated the genetic isolation of these two races using strains from the maize (Z strain) and mugwort (E strain) races selected for diagnostic alleles at two allozyme loci. In a cage containing maize and mugwort plants and located in natural conditions, mating between individuals of the same strain occurred more often than mating between males and females of the E and Z strains. In particular, we obtained no evidence for crosses between Z females and E males. We also found that females of the Z strain laid their eggs almost exclusively on maize, whereas females of the E strain laid their eggs preferentially, but not exclusively, on mugwort. These results suggest that the genetic differentiation between the two host races may also be favored by host-plant preference, one of the first steps toward sympatric speciation.

Evolution of disassortative and assortative mating preferences based on imprinting

A two-locus haploid model of sexual selection is investigated to explore evolution of disassortative and assortative mating preferences based on imprinting. In this model, individuals imprint on a genetically transmitted trait during early ontogeny and choosy females later use those parental images as a criterion of mate choice. It is assumed that the presence or absence of the female preference is determined by a genetic locus. In order to incorporate such mechanisms as inbreeding depression and heterozygous advantage into our haploid framework, we assume that same-type matings are less fertile than different-type mating. The model suggests that: if all the females have a disassortative mating preference a viability-reducing trait may be maintained even without the fertility cost of same-type matings; a disassortative mating preference can be established even if it is initially rare, when there is a fertility cost of same-type matings. Further, an assortative mating preference is less likely to evolve than a disassortative mating preference. The model may be applicable to the evolution of MHC-disassortative mating preferences documented in house mice and humans.

Gall Flies, Inquilines, and Goldenrods: A Model for Host-race Formation and Sympatric Speciation

Host shifts and subsequent host-race formation likely play a more common role in the speciation of herbivorous insects than has generally been recognized. Our studies of the interactions of goldenrod host plants (Solidago: Compositae), the gall fly Eurosta solidaginis (Diptera: Tephritidae), and the stem- and gall-boring Mordellistena convicta (Coleoptera: Mordellidae) provide behavioral, ecological, and genetic evidence of insect host races that may represent incipient species formed via sympatric speciation. Eurosta solidaginis has developed genetically differentiated and reproductively isolated host races that are associated with the ancestral host Solidago altissima and the derived host S. gigantea. Conventional wisdom suggests that shifts even to closely related host plants are limited by host preferences or the inability to utilize a chemically and developmentally distinct host. However, our preliminary work with Eurosta from S. gigantea implies that host choice and gall induction do not deter a shift to S. canadensis. The galling of Solidago by Eurosta created a new resource that has led to a subsequent host range expansion by the stem-boring beetle. Mordellistena convicta from stems and galls are genetically distinct and likely shifted from stems to galls. Beetles from S. altissima versus S. gigantea galls exhibit assortative mating and higher preference for and/or performance on their natal host. The present-day distributions of the Eurosta host races and their behavioral isolating mechanisms do not suggest that geographic isolation was required for their formation; rather these characteristics suggest a sympatric mode of differentiation. Our findings lend credence to recent assertions that sympatric speciation may be an important source of biodiversity.

Gall Flies, Inquilines, and Goldenrods: A Model for Host-race Formation and Sympatric Speciation1

SYNOPSIS. Host shifts and subsequent host-race formation likely play a more common role in the speciation of herbivorous insects than has generally been recognized. Our studies of the interactions of goldenrod host plants (Solidago: Compositae), the gall fly Eurosta solidaginis (Diptera: Tephritidae), and the stem- and gall-boring Mordellistena convicta (Coleoptera: Mordellidae) provide behavioral, ecological, and genetic evidence of insect host races that may represent incipient species formed via sympatric speciation. Eurosta solidaginis has developed genetically differentiated and reproductively isolated host races that are associated with the ancestral host Solidago altissima and the derived host S. gigantea. Conventional wisdom suggests that shifts even to closely related host plants are limited by host preferences or the inability to utilize a chemically and developmentally distinct host. However, our preliminary work with Eurosta from S. gigantea implies that host choice and gall induction do not deter a shift to S. canadensis. The galling of Solidago by Eurosta created a new resource that has led to a subsequent host range expansion by the stem-boring beetle. Mordellistena convicta from stems and galls are genetically distinct and likely shifted from stems to galls. Beetles from S. altissima versus S. gigantea galls exhibit assortative mating and higher preference for and/or performance on their natal host. The present-day distributions of the Eurosta host races and their behavioral isolating mechanisms do not suggest that geographic isolation was required for their formation; rather these characteristics suggest a sympatric mode of differentiation. Our findings lend credence to recent assertions that sympatric speciation may be an important source of biodiversity.

Cytoplasmic incompatibility in Drosophila populations: Influence of assortative mating on symbiont distribution

Cytoplasmic incompatibility is known to occur between strains of both Drosophila simulans and D. melanogaster. Incompatibility is associated with the infection of Drosophila with microorganismal endosymbionts. This paper reports survey work conducted on strains of D. simulans and D. melanogaster from diverse geographical locations finding that infected populations are relatively rare and scattered in their distribution. The distribution of infected populations of D. simulans appears to be at odds with deterministic models predicting the rapid spread of the infection through uninfected populations. Examination of isofemale lines from four localities in California where populations appear to be polymorphic for the infection failed to find evidence for consistent assortative mating preferences between infected and uninfected populations that may explain the basis for the observed polymorphism.

Some Problems and Approaches in Avian Mate Choice

Some Problems and Approaches in Avian Mate Choice

MALE MATING PREFERENCES AND ASSORTATIVE MATING IN THE SOLDIER BEETLE.

Mating preferences for a color characteristic were examined in three northern Georgia populations of the soldier beetle, Chauliognathus pennsylvanicus De Geer, by comparing observed and expected frequencies of matings to the same phenotype. The three populations are apparently in a zone of secondary contact between disparate color morphs. In the most northern population sampled, preferences were strong and were associated with positive assortative mating with respect to the color characteristic. In the southern population, neither assortative mating nor mating preference was strong, while in the middle population, preferences were expressed in the absence of assortative mating. Mating preferences cannot be attributed to host-plant choice, microhabitat choice, or simple conditioning on the phenotype of the last mate. However, they may represent part of a specific mate-recognition system which has been maintained in part of the zone of overlap but which has eroded in other areas.

Estimation of assortative mating preferences in the Arctic skua.

Methods are described for the maximum likelihood estimation of mating preferences in models of assortative mating for monogamous and polygamous organisms. These methods are applied to data of matings of the three phenotypes, pale, intermediated and dark of the Arctic Skua. The data were obtained by exhaustive surveys of the Arctic Skua populations on the islands of Fair Isle and Foula. The data give evidence of significant assortative mating of pale birds on Foula and intermediate birds on Fair Isle. The combined data show that there is very highly significant assortative mating, but only of intermediates. In previous surveys, data, in which intermediates and darks were not distinguished, were obtained from a number of islands in the Shetlands. These data, combined with the present data, show that the overall assortative mating of pale is very highly significant with no evidience of heterogeneity. The assortative mating of intermediate birds on Fair Isle agrees with other evidence showing that inermediate males have an advantage as a result of sexual selection.