Alternative male mating tactics of the substrate brooding cichlid Telmatochromis temporalis in Lake Tanganyika

Male alternative reproductive tactics and sperm competition: a meta-analysis

In many animal species, males may exhibit one of several discrete, alternative ways of obtaining fertilisations, known as alternative reproductive tactics (ARTs). Males exhibiting ARTs typically differ in the extent to which they invest in traits that improve their mating success, or the extent to which they face sperm competition. This has led to the widespread prediction that males exhibiting ARTs associated with a high sperm competition risk, or lower investment into traits that improve their competitiveness before mating, should invest more heavily into traits that improve their competitiveness after mating, such as large ejaculates and high-quality sperm. However, despite many studies investigating this question since the 1990s, evidence for differences in sperm and ejaculate investment between male ARTs is mixed, and there has been no quantitative summary of this field. Following a systematic review of the literature, we performed a meta-analysis examining how testes size, sperm number and sperm traits differ between males exhibiting ARTs that face either a high or low sperm competition risk, or high or low investment in traits that increase mating success. We obtained data from 92 studies and 67 species from across the animal kingdom. Our analyses showed that male fish exhibiting ARTs facing a high sperm competition risk had significantly larger testes (after controlling for body size) than those exhibiting tactics facing a low sperm competition risk. However, this effect appears to be due to the inappropriate use of the gonadosomatic index as a body-size corrected measure of testes investment, which overestimates the difference in testes investment between male tactics in most cases. We found no significant difference in sperm number between males exhibiting different ARTs, regardless of whether sperm were measured from the male sperm stores or following ejaculation. We also found no significant difference in sperm traits between males exhibiting different ARTs, with the exception of sperm adenosine triphosphate (ATP) content in fish. Finally, the difference in post-mating investment between male ARTs was not influenced by the extent to which tactics were flexible, or by the frequency of sneakers in the population. Overall, our results suggest that, despite clear theoretical predictions, there is little evidence that male ARTs differ substantially in investment into sperm and ejaculates across species. The incongruence between theoretical and empirical results could be explained if (i) theoretical models fail to account for differences in overall resource levels between males exhibiting different ARTs or fundamental trade-offs between investment into different ejaculate and sperm traits, and (ii) studies often use sperm or ejaculate traits that do not reflect overall post-mating investment accurately or affect fertilisation success.

Nest defense in the face of cuckoldry: evolutionary rather than facultative adaptation to chronic paternity loss

Background

Raising unrelated offspring is typically wasteful of parental resources and so individuals are expected to reduce or maintain low levels of parental effort when their parentage is low. This can involve facultative, flexible adjustments of parental care to cues of lost parentage in the current brood, stabilizing selection for a low level of paternal investment, or an evolutionary reduction in parental investment in response to chronically low parentage.

Results

We studied parental care in Variabilichromis moorii, a socially monogamous, biparental cichlid fish, whose mating system is characterized by frequent cuckoldry and whose primary form of parental care is offspring defense. We combine field observations with genetic parentage analyses to show that while both parents defend their nest against intruding con- and hetero-specifics, males and females may do so for different reasons. Males in the study group (30 breeding pairs) sired 0–100% (median 83%) of the fry in their nests. Males defended less against immediate threats to the offspring, and more against threats to their territories, which are essential for the males’ future reproductive success. Males also showed no clear relationship between their share of defense and their paternity of the brood. Females, on the other hand, were related to nearly all the offspring under their care, and defended almost equally against all types of threats.

Conclusion

Overall, males contributed less to defense than females and we suggest that this asymmetry is the result of an evolutionary response by males to chronically high paternity loss in this species. Although most males in the current study group achieved high parentage in their nests, the average paternity in V. moorii, sampled across multiple seasons, is only about 55%. We highlight the importance and complexity of studying nest defense as a form of parental care in systems where defense may serve not only to protect current offspring, but also to ensure future reproductive success by maintaining a territory.

Brood-tending males in a biparental fish suffer high paternity losses but rarely cuckold

Extra‐pair paternity within socially monogamous mating systems is well studied in birds and mammals but rather neglected in other animal taxa. In fishes, social monogamy has evolved several times but few studies have investigated the extent to which pair‐bonded male fish lose fertilizations to cuckolders and gain extra‐pair fertilizations themselves. We address this gap and present genetic paternity data collected from a wild population of Variabilichromis moorii, a socially monogamous African cichlid with biparental care of offspring. We show that brood‐tending, pair‐bonded males suffer exceptionally high paternity losses, siring only 63% of the offspring produced by their female partners on average. The number of cuckolders per brood ranged up to nine and yet, surprisingly, brood‐tending males in the population were rarely the culprits. Brood‐tending males sired very few extra‐pair offspring, despite breeding in close proximity to one another. While unpaired males were largely responsible for the cuckoldry, pair‐bonded males still enjoyed higher fertilization success than individual unpaired males. We discuss these results in the context of ecological and phenotypic constraints on cuckoldry and the fitness payoffs of alternative male tactics. Our study provides new insights into how pair‐bonded males handle the trade‐off between securing within‐pair and extra‐pair reproduction.

Species-specific patterns of nonapeptide brain gene expression relative to pair-bonding behavior in grouping and non-grouping cichlids

Comparative studies have revealed that vasopressin-oxytocin pathways are associated with both pair bonding and grouping behavior. However, the relationship between pair bonding and grouping behavior remains unclear. In this study, our aim was to identify whether two species that differ in grouping behavior display a corresponding difference in their pair bonds, and in the underlying vasopressin-oxytocin hormonal pathways. Using two species of cichlid fishes, the highly social Neolamprologus pulcher and the non-social Telmatochromis temporalis, we measured proximity of pairs during pair bond formation, and then measured social behaviors (proximity, aggression, submission, affiliation) and brain gene expression of isotocin and arginine vasotocin (the teleost homologues of oxytocin and vasopressin, respectively), as well as their receptors, after a temporary separation and subsequent reunion of the bonded pairs. Pairs of the social species spent more time in close proximity relative to the non-social species. Rates of aggression increased in both species following the separation and reunion treatment, relative to controls that were not separated. Overall, whole brain expression of isotocin was higher in the social species relative to the non-social species, and correlated with proximity, submission, and affiliation, but only in the social species. Our results suggest that both a social and a non-social cichlid species have similar behavioral responses to a temporary separation from a mate, and we found no difference in the brain gene expression of measured hormones and receptors based on our separation-reunion treatment. However, our results highlight the importance of isotocin in mediating submissive and affiliative behaviors in cichlid fishes, and demonstrate that isotocin has species-specific correlations with socially relevant behaviors.

No experimental evidence for sneaking in a west african cichlid fish with extremely long sperm

Alternative reproductive tactics are widespread in fishes, increasing the potential for sperm competition. Sperm competition has enormous impact on both variation in sperm numbers and sperm size. In cichlids, the sperm competition risk is very divergent and longer sperm are usually interpreted as adaptation to sperm competition. Here we examined whether sneaking tactics exist in Pelvicachromis taeniatus, a socially monogamous cichlid with biparental brood care from West Africa. The small testis indicates low gonadal investment which is typical for genetically monogamous species. In contrast, sperm length with up to 85 μm is extraordinarily long. We examined the reproductive behaviour of ten groups with a male-biased sex ratio under semi-natural conditions via continuous video recording. We recorded spawning site preferences and correlates of reproductive success and conducted paternity tests using microsatellites. Safe breeding sites that could be successfully defended were preferred. All offspring could be assigned to their parents and no multiple paternities were detected. Body size of spawning pairs predicted their spawning probability and offspring hatching rate suggesting benefits from mating with large individuals. Our study suggests low risk of sperm competition under the given conditions in P. taeniatus and thus first evidence for genetic monogamy in a substrate breeding cichlid.

Two patterns of parasitic male mating behaviors and their reproductive success in Japanese medaka, Oryzias latipes

We found two patterns of parasitic mating behaviors by male in Japanese medaka, Oryzias latipes, in the spawning by one female and two males in the aquarium condition. In the first type of parasitic mating behavior, the unpaired male would rush toward the closely adhering female and paired male, and simultaneously perform emission behavior with close adhesion to the female (simultaneous emission). The second type of parasitic mating behavior was that the unpaired male would rush toward the female with spawned eggs hanging down from the genital pore several seconds after pair-spawning, perform emission behavior with close adhesion to the female without any prespawning behavior (post-spawn emission). The frequencies of "simultaneous emission" and "post-spawn emission" were 20 (19.6%) and 18 cases (17.7%), respectively, in 102 trials, and the average reproductive successes about 41% and 20%, respectively. The reproductive success of simultaneous emission was not correlated with the timing and duration of spawning behaviors of the paired/ unpaired male, while the reproductive success of post-spawn emission significantly decreased as the length of time during which the paired male adhered to female increased. Observations of two consecutive spawning behaviors using same combination of two males revealed that paired males always tend to become paired males. However, the role of both males was occasionally reversed, indicating flexibility in mating tactics.

Alternative Reproductive Tactics in the Shell-Brooding Lake Tanganyika Cichlid Neolamprologus brevis

Alternative reproductive tactics (ARTs) are found in several Lake Tanganyika shell-brooding cichlids. Field studies were conducted in the Wonzye population to examine reproductive ecology and ARTs in the Lake Tanganyika shell-brooding cichlid Neolamprologus brevis. We discovered that this fish occurred in both rocky- and sandy-bottom habitats, but in rocky habitats, brood-caring females exclusively occurred in shell-patches that another cichlid species created. All N. brevis of both sexes in the patches were sexually mature, whereas immature males and females with unripe eggs were found frequently in sandy-bottom habitats. Males in sandy-bottom habitats were smaller, but fed more frequently and were in better somatic condition than males in the patches. Similar tendency was found in females. This indicates that N. brevis uses different habitats depending on the stage of its life history, with migration from sandy-bottom habitats to the shell-patches for reproduction. Males in the patches exhibited different behavior patterns: floating above the patches and lying in the patches. The former was larger, more aggressive, and invested less in gonads (relative to body size) than the latter. These results accord with those of other shell-brooding Lake Tanganyika cichlids with ARTs, and they therefore suggest the presence of ARTs in N. brevis.

Mating and Parental Care in Lake Tanganyika's Cichlids

Cichlid fishes of Lake Tanganyika display a variety of mating and parental care behaviors, including polygamous and monogamous mouthbrooding and substrate breeding, cooperative breeding, as well as various alternative reproductive tactics such as sneaking and piracy. Moreover, reproductive behaviors sometimes vary within species both in space and in time. Here, I survey reports on mating and parenting behaviors of Lake Tanganyika cichlid species and address the evolution of mating and parental care patterns and sexual dimorphism. Notes on measures of sexual selection intensity and the difficulties of defining mating systems and estimating selection intensities at species level conclude the essay.

Evolutionary history of the Lake Tanganyika cichlid tribe Lamprologini (Teleostei: Perciformes) derived from mitochondrial and nuclear DNA data

Lake Tanganyika comprises a cichlid species flock with substrate-breeding and mouthbrooding lineages. While sexual selection via mate choice on male mating color is thought to boost speciation rates in mouthbrooding cichlids, this is not the case in substrate-breeding lamprologines, which mostly form stable pairs and lack sexual dichromatism. We present a comprehensive reconstruction of the evolution of the cichlid tribe Lamprologini, based upon mtDNA sequences and multilocus nuclear DNA (AFLP) markers. Twelve mtDNA clades were identified, seven of which were corroborated by the AFLP tree. The radiation is likely to have started about 5.3 MYA, contemporarily with that of the mouthbrooding C-lineage, and probably triggered by the onset of deep-water conditions in Lake Tanganyika. Neither the Congo- nor the Malagarazi River species form the most ancestral branch. Several conflicts in the mtDNA phylogeny with taxonomic assignments based upon color, eco-morphology and behavior could be resolved and complemented by the AFLP analysis. Introgressive hybridization upon secondary contact seems to be the most likely cause for paraphyly of taxa due to mtDNA capture in species involving brood-care helpers, while accidental hybridization best explains the para- or polyphyly of several gastropod shell breeders. Taxonomic error or paraphyly due to the survival of ancestral lineages appear responsible for inconsistencies in the genera Lamprologus and Neolamprologus.

Reproductive parasitism: male and female responses to conspecific and heterospecific intrusions at spawning in a mouth-brooding cichlid Ophthalmotilapia ventralis

A rare form of alternative reproductive behaviour without simultaneous parasitic spawning was observed in Ophthalmotilapia ventralis, a lekking mouth-brooding cichlid from Lake Tanganyika. Floater males attempted to sneak opportunistically into the territory to actively court the female, while the owner (bourgeois male) defended the territory against other potential intruders. Floater males had more body fat than territory owners and generally higher condition factors. In field experiments, the response of bourgeois males and courted females was tested towards floaters and egg predators (a catfish Synodontis multipunctatus) present in the territories. Territory owners responded aggressively particularly to floaters, and female responsiveness to bourgeois male courtship tended to decline when floaters were present. The potential influence of reproductive parasitism on sexual selection in mouth-brooding cichlids is discussed.

Ongoing ecological divergence in an emerging genomic model

Much of Earth's biodiversity has arisen through adaptive radiation. Important avenues of phenotypic divergence during this process include the evolution of body size and life history (Schluter 2000). Extensive adaptive radiations of cichlid fishes have occurred in the Great Lakes of Africa, giving rise to behaviours that are remarkably sophisticated and diverse across species. In Tanganyikan shell-brooding cichlids of the tribe Lamprologini, tremendous intraspecific variation in body size accompanies complex breeding systems and use of empty snail shells to hide from predators and rear offspring. A study by Takahashi et al. (2009) in this issue of Molecular Ecology reveals the first case of genetic divergence between dwarf and normal-sized morphs of the same nominal lamprologine species, Telmatochromis temporalis. Patterns of population structure suggest that the dwarf, shell-dwelling morph of T. temporalis might have arisen from the normal, rock-dwelling morph independently in more than one region of the lake, and that pairs of morphs at different sites may represent different stages early in the process of ecological speciation. The findings of Takahashi et al. are important first steps towards understanding the evolution of these intriguing morphs, yet many questions remain unanswered about the mating system, gene flow, plasticity and selection. Despite these limitations, descriptive work like theirs takes on much significance in African cichlids due to forthcoming resources for comparative genomics.

Evidence for divergent natural selection of a Lake Tanganyika cichlid inferred from repeated radiations in body size

Divergent natural selection is thought to play a vital role in speciation, but clear, measurable examples from nature are still few. Among the many possible sources of divergent natural selection, predation pressure may be important because predators are ubiquitous in food webs. Here, we show evidence for divergent natural selection in a Lake Tanganyika cichlid, Telmatochromis temporalis, which uses burrows under stones or empty snail shells as shelters. This species contains normal and dwarf morphs at several localities. The normal morph inhabits rocky shorelines, whereas the dwarf morph invariably inhabits shell beds, where empty snail shells densely cover the lake bottom. Genetic evidence suggested that the dwarf morph evolved independently from the normal morph at two areas, and morphological analysis and evaluation of habitat structure revealed that the body sizes of morphs closely matched the available shelter sizes in their habitats. These findings suggest that the two morphs repeatedly evolved through divergent natural selection associated with the strategy for sheltering from predators.

Monogamy in the maternally mouthbrooding Lake Tanganyika cichlid fish Tropheus moorii

Supported by evidence for assortative mating and polygynandry, sexual selection through mate choice was suggested as the main force driving the evolution of colour diversity of haplochromine cichlids in Lakes Malawi and Victoria. The phylogenetically closely related tribe Tropheini of Lake Tanganyika includes the genus Tropheus, which comprises over 100 colour variants currently classified into six morphologically similar, polyphyletic species. To assess the potential for sexual selection in this sexually monochromatic maternal mouthbrooder, we used microsatellite-based paternity inference to investigate the mating system of Tropheus moorii. In contrast to haplochromines in Lake Malawi, multiple paternity is rare or even absent in broods of T. moorii. Eighteen of the 19 analysed families were consistent with genetic monogamy, while either a mutation or more than one sire explained the genotype of one offspring in another brood. We discuss the differences in breeding behaviour between T. moorii and the Lake Malawi haplochromines, and evaluate additional factors or alternatives to sexual selection as promoters of colour diversification. A preliminary survey of other Tropheini species suggested that multiple paternity is infrequent in the entire tribe.