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Assortative mating among Lake Malawi cichlid fish populations is not simply predictable from male nuptial colour.

Blais J, Plenderleith M, Rico C, Taylor MI, Seehausen O, van Oosterhout C, Turner GF - BMC Evol. Biol. (2009)

Bottom Line: Here, we tested predictions from the hypothesis that allopatric divergence in male colour is associated with corresponding divergence in preference.Surprisingly, laboratory mate choice experiments revealed significant assortative mating not only between population pairs with differently coloured males, but between population pairs with similarly-coloured males too.Future speciation models aimed at explaining African cichlid radiations may therefore consider incorporating such mating cues in mate choice scenarios.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, University of Hull, Hull HU6 7RX, UK. jonatan.blais.1@ulaval.ca

ABSTRACT

Background: Research on the evolution of reproductive isolation in African cichlid fishes has largely focussed on the role of male colours and female mate choice. Here, we tested predictions from the hypothesis that allopatric divergence in male colour is associated with corresponding divergence in preference.

Methods: We studied four populations of the Lake Malawi Pseudotropheus zebra complex. We predicted that more distantly-related populations that independently evolved similar colours would interbreed freely while more closely-related populations with different colours mate assortatively. We used microsatellite genotypes or mesh false-floors to assign paternity. Fisher's exact tests as well as Binomial and Wilcoxon tests were used to detect if mating departed from random expectations.

Results: Surprisingly, laboratory mate choice experiments revealed significant assortative mating not only between population pairs with differently coloured males, but between population pairs with similarly-coloured males too. This suggested that assortative mating could be based on non-visual cues, so we further examined the sensory basis of assortative mating between two populations with different male colour. Conducting trials under monochromatic (orange) light, intended to mask the distinctive male dorsal fin hues (blue v orange) of these populations, did not significantly affect the assortative mating by female P. emmiltos observed under control conditions. By contrast, assortative mating broke down when direct contact between female and male was prevented.

Conclusion: We suggest that non-visual cues, such as olfactory signals, may play an important role in mate choice and behavioural isolation in these and perhaps other African cichlid fish. Future speciation models aimed at explaining African cichlid radiations may therefore consider incorporating such mating cues in mate choice scenarios.

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Map of Lake Malawi showing sampling sites of study populations. Male (a) and female (b) Pseudotropheus emmiltos (northern orange) from Mphanga Rocks; male (c) and female (d) Pseudotropheus zebra (northern blue) from Nkhata Bay; male (e) and female (f) Pseudotropheus zebra (southern blue) fromChiofu Bay and male (g) and female (h) Pseudotropheus thapsinogen (southern orange) from Eccles Reef.
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Figure 1: Map of Lake Malawi showing sampling sites of study populations. Male (a) and female (b) Pseudotropheus emmiltos (northern orange) from Mphanga Rocks; male (c) and female (d) Pseudotropheus zebra (northern blue) from Nkhata Bay; male (e) and female (f) Pseudotropheus zebra (southern blue) fromChiofu Bay and male (g) and female (h) Pseudotropheus thapsinogen (southern orange) from Eccles Reef.

Mentions: The study populations were members of the Pseudotropheus zebra species complex, cichlid fish endemic to Lake Malawi. The taxonomy of this group is confused, and these fish are sometimes assigned to the genus or subgenus Maylandia or the genus Metriaclima. Many allopatric colour variants have been assigned species names, while others have not. Territorial males of all four study populations are pale blue with strongly contrasting black vertical bars, but populations differ in the colour of the dorsal fin. Male P. zebra from Nkhata Bay (11°36'S, 34°18'E) on the northwestern shore and Chiofu Bay (13°13'S, 34°52'E) on the southeastern shore have blue dorsal fins (henceforth referred to as 'northern blue' and 'southern blue', respectively). Male P. thapsinogen from Chimwalani (Eccles) Reef (13°46'S, 34°58'E) off the southeastern shore and male P. emmiltos from Mpanga Rocks (10° 25'S 34°16'E) near the northwestern shore have orange dorsal fins and are referred to as 'southern orange' and 'northern orange', respectively (Figure 1). P. thapsinogen (southern orange) males have yellow throat membranes, whereas those of the northern orange males (P. emmiltos) are dark grey. These throat membranes are normally not visible unless protruded beneath the gill-cover as part of a lateral display. However, these displays are typically part of antagonistic rather than courtship interactions, and therefore it is unlikely that females use this trait in mate choice. The taxonomy, morphology and ecology of these populations were discussed by Stauffer et al. [30] and the biology of these and related 'mbuna' species reviewed by Genner & Turner [31]. Fish used were wild-caught, although some first-generation laboratory stock bred from wild-caught parents were used in experiment 2. Housing and maintenance conditions have been described previously [6,29].


Assortative mating among Lake Malawi cichlid fish populations is not simply predictable from male nuptial colour.

Blais J, Plenderleith M, Rico C, Taylor MI, Seehausen O, van Oosterhout C, Turner GF - BMC Evol. Biol. (2009)

Map of Lake Malawi showing sampling sites of study populations. Male (a) and female (b) Pseudotropheus emmiltos (northern orange) from Mphanga Rocks; male (c) and female (d) Pseudotropheus zebra (northern blue) from Nkhata Bay; male (e) and female (f) Pseudotropheus zebra (southern blue) fromChiofu Bay and male (g) and female (h) Pseudotropheus thapsinogen (southern orange) from Eccles Reef.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2667177&req=5

Figure 1: Map of Lake Malawi showing sampling sites of study populations. Male (a) and female (b) Pseudotropheus emmiltos (northern orange) from Mphanga Rocks; male (c) and female (d) Pseudotropheus zebra (northern blue) from Nkhata Bay; male (e) and female (f) Pseudotropheus zebra (southern blue) fromChiofu Bay and male (g) and female (h) Pseudotropheus thapsinogen (southern orange) from Eccles Reef.
Mentions: The study populations were members of the Pseudotropheus zebra species complex, cichlid fish endemic to Lake Malawi. The taxonomy of this group is confused, and these fish are sometimes assigned to the genus or subgenus Maylandia or the genus Metriaclima. Many allopatric colour variants have been assigned species names, while others have not. Territorial males of all four study populations are pale blue with strongly contrasting black vertical bars, but populations differ in the colour of the dorsal fin. Male P. zebra from Nkhata Bay (11°36'S, 34°18'E) on the northwestern shore and Chiofu Bay (13°13'S, 34°52'E) on the southeastern shore have blue dorsal fins (henceforth referred to as 'northern blue' and 'southern blue', respectively). Male P. thapsinogen from Chimwalani (Eccles) Reef (13°46'S, 34°58'E) off the southeastern shore and male P. emmiltos from Mpanga Rocks (10° 25'S 34°16'E) near the northwestern shore have orange dorsal fins and are referred to as 'southern orange' and 'northern orange', respectively (Figure 1). P. thapsinogen (southern orange) males have yellow throat membranes, whereas those of the northern orange males (P. emmiltos) are dark grey. These throat membranes are normally not visible unless protruded beneath the gill-cover as part of a lateral display. However, these displays are typically part of antagonistic rather than courtship interactions, and therefore it is unlikely that females use this trait in mate choice. The taxonomy, morphology and ecology of these populations were discussed by Stauffer et al. [30] and the biology of these and related 'mbuna' species reviewed by Genner & Turner [31]. Fish used were wild-caught, although some first-generation laboratory stock bred from wild-caught parents were used in experiment 2. Housing and maintenance conditions have been described previously [6,29].

Bottom Line: Here, we tested predictions from the hypothesis that allopatric divergence in male colour is associated with corresponding divergence in preference.Surprisingly, laboratory mate choice experiments revealed significant assortative mating not only between population pairs with differently coloured males, but between population pairs with similarly-coloured males too.Future speciation models aimed at explaining African cichlid radiations may therefore consider incorporating such mating cues in mate choice scenarios.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, University of Hull, Hull HU6 7RX, UK. jonatan.blais.1@ulaval.ca

ABSTRACT

Background: Research on the evolution of reproductive isolation in African cichlid fishes has largely focussed on the role of male colours and female mate choice. Here, we tested predictions from the hypothesis that allopatric divergence in male colour is associated with corresponding divergence in preference.

Methods: We studied four populations of the Lake Malawi Pseudotropheus zebra complex. We predicted that more distantly-related populations that independently evolved similar colours would interbreed freely while more closely-related populations with different colours mate assortatively. We used microsatellite genotypes or mesh false-floors to assign paternity. Fisher's exact tests as well as Binomial and Wilcoxon tests were used to detect if mating departed from random expectations.

Results: Surprisingly, laboratory mate choice experiments revealed significant assortative mating not only between population pairs with differently coloured males, but between population pairs with similarly-coloured males too. This suggested that assortative mating could be based on non-visual cues, so we further examined the sensory basis of assortative mating between two populations with different male colour. Conducting trials under monochromatic (orange) light, intended to mask the distinctive male dorsal fin hues (blue v orange) of these populations, did not significantly affect the assortative mating by female P. emmiltos observed under control conditions. By contrast, assortative mating broke down when direct contact between female and male was prevented.

Conclusion: We suggest that non-visual cues, such as olfactory signals, may play an important role in mate choice and behavioural isolation in these and perhaps other African cichlid fish. Future speciation models aimed at explaining African cichlid radiations may therefore consider incorporating such mating cues in mate choice scenarios.

Show MeSH