Territoriality and nutritional condition in Cynotilapia afra (Gunther) and Pseudotropheus zebra (Boulenger), cichlidae in Lake Malawi National Park, Malawi

The standard length, diurnal activities, territory sizes, and areas over which individuals foraged and the nutritional condition of territorial and non-territorial Cynotilapia afra and Pseudotropheus zebra were compared. Results show that territorial tenureship in these fishes does not depend on the male size, implying that aggressiveness, experience and motivation are more important in the maintenance of territory. However, terri-toriality in C. afra (t = 10.93, P < 0.05) and P. zebra (t = 3.31, P < 0.05) manifests itself in the reduction of nutritional condition because territorial males engage in energetically more demanding activities, e.g. courtship displays, fertilizing ripe females and chasing intruders that trespass into their territories. Territorial C. afra (t = 4.77; P < 0.05) and P. zebra (t = 5.89; P < 0.05) also fed over significantly smaller areas and spent significantly less time feeding than did non-territorial males. The biological significance of territoriality in these fish species is therefore not food intake, but mate attraction and reproductive success for which they trade off their nutritional condition. However, there might be a nutritional threshold below which the cost out-weighs the benefit. Hence, territorial males in poorer health abandon their territories in order to regain their condition.     

Functional and Genetic Integration in the Skulls of Lake Malawi Cichlids

The level of integration present among organismal traits is thought to influence evolutionary potential, and this potential should be affected by the type or types of integration displayed (e.g., functional, developmental, or genetic). Morphological integration is generally high among functionally related traits, but whether this is predominantly determined by genetic architecture, or is instead a result of biomechanical remodeling during development remains poorly understood. We examine this question in Lake Malawi cichlid fishes by combining a finite-element analysis (FEA) of bite force transmission with quantitative genetic analyses of skull morphology in order to test the hypothesis that functionally coupled traits share a common genetic basis. FEA modeling indicates that the profile of the neurocranium affects its ability to resist forces transmitted from the jaws during biting, and suggests a novel role for skull shape in fish feeding mechanics. Quantitative trait loci mapping demonstrates that the functional integration between jaw and neurocranial shape has a genetic basis, and that this association is being driven by alleles inherited from the specialized biting species. Notably, the co-inheritance of these two functionally related traits in our F₂ matches patterns of covariation within and between Lake Malawi cichlid species. Across species, jaw and neurocranial shapes covary, but the trend appears strongest among biting species. Similarly, within populations of biting species, the dimensions of the jaw and neurocranium are tightly linked, whereas this correlation disappears within populations of omnivorous and suction feeding fish. These data suggest (1) that either pleiotropy, or physical linkage maintained by selection, underlies the phenotypic integration of these two functionally related traits, and (2) that this pattern of integration may have influenced the radiation of craniofacial morphology in Lake Malawi cichlids.     

Elevated mtDNA diversity in introduced populations of Cynotilapia afra (Günther 1894) in Lake Malawi National Park is evidence for multiple source populations and hybridization

Genetic variation in many invasive species shows little or no signs of a founder event, suggesting that high genetic diversity may facilitate establishment success. The rocky‐shore, plankton‐feeding cichlid fish Cynotilapia afra is endemic to Lake Malawi, but naturally absent from many suitable sites. In the 1960s, this species was introduced to the southern areas of the lake, presumably as a result of the aquarium fish trade. It has now become established on a number of rocky areas within the Lake Malawi National Park. Here, we analysed DNA sequence variation in the mitochondrial control region of six native and four introduced populations of C. afra, and three populations of the closely‐related and hybridizing Pseudotropheus zebra. In contrast to previous studies of Lake Malawi rock dwelling cichlids, network analyses suggested that native populations of C. afra showed high levels of lineage sorting in mtDNA. Introduced populations showed higher sequence and haplotype diversity than their native counterparts. Our analyses suggested that the elevated gene diversity was largely attributed to the fact that the introduced C. afra populations were derived from several genetically distinct and geographically separate populations, and to a lesser extent because of introgressive hybridization with native P. zebra. The establishment and spread of C. afra may be partly because of its ability to occupy a vacant ecological niche, but it may also have been facilitated by its enhanced genetic diversity.     

Cross-fostering Does Not Influence the Mate Preferences and Territorial Behaviour of Males in Lake Victoria Cichlids

The ability to recognise conspecifics in contexts of mate choice and territorial defence may have large effects on an individual's fitness. Understanding the development of assortative behaviour may shed light on how species assortative behaviour evolves and how it may influence reproductive isolation. This is the case not only for female mate preferences, but also for male mate preferences and male territorial behaviour. Here we test with a cross-fostering experiment whether early learning influences male mate preferences and male–male aggression biases in two closely related, sympatrically occurring cichlid species Pundamilia pundamilia and Pundamilia nyererei from Lake Victoria. Males that had been fostered, either by a conspecific female or by a heterospecific female, were tested for their aggression bias, as well as for their mate preferences, in two-way choice tests. Males cross-fostered with conspecific and heterospecific foster mothers selectively directed their aggression towards conspecific intruders. The cross-fostering treatment also did not affect male mate preferences. These results are in striking contrast with the finding that females of these species show a sexual preference for males of the foster species.     

Mate Choice Copying in Humans

There is substantial evidence that in human mate choice, females directly select males based on male display of both physical and behavioral traits. In non-humans, there is additionally a growing literature on indirect mate choice, such as choice through observing and subsequently copying the mating preferences of conspecifics (mate choice copying). Given that humans are a social species with a high degree of sharing information, long-term pair bonds, and high parental care, it is likely that human females could avoid substantial costs associated with directly searching for information about potential males by mate choice copying. The present study was a test of whether women perceived men to be more attractive when men were presented with a female date or consort than when they were presented alone, and whether the physical attractiveness of the female consort affected women’s copying decisions. The results suggested that women’s mate choice decision rule is to copy only if a man’s female consort is physically attractive. Further analyses implied that copying may be a conditional female mating tactic aimed at solving the problem of informational constraints on assessing male suitability for long-term sexual relationships, and that lack of mate choice experience, measured as reported lifetime number of sex partners, is also an important determinant of copying.     

Sexual Selection and Mate Choice

After a long period of dormancy, Darwin's theory of sexual selection in general, and mate choice in particular, now represents one of the most active fields in evolutionary research. After a brief overview of the history of ideas and a short introduction into the main mechanisms of sexual selection, I discuss some recent theoretical developments and empirical findings in the study of mate choice and review the various current models of mate choice, which can be grossly divided into adaptive models and nonadaptive models. I also examine whether available primate evidence supports various hypotheses concerning mate choice. Although primatologists were long aware that nonhuman primates have preferences for certain mating partners, until recently the functions and evolutionary consequences of their preferences remained obscure. Now there is growing evidence that mate choice decisions provide primates with important direct or indirect benefits. For example, several observations are consistent with the hypothesis that by direct or indirect mate choice female primates lower the risk of infanticide or enhance the chance of producing viable offspring. Nevertheless, there are also significant holes in our knowledge. How the male mandrill, one of Darwin's famous examples, got his brightly colored face, is still unknown.     

Mate Choice in Non-Human Primates

Mate choice has been observed in many species of non-human primates.There are few definitive studies, however, due to the long lifespans, complex social behavior, and cognitive abilities of theseanimals. Here I review the current literature on mate choicein primates. Females typically prefer complex behavioral traitssuch as social status, familiarity, personality, and parentalcare abilities. This tendency to prefer behavioral traits isconsistent with the non-primate mammalian data. A female's abilityto express preferences, however, is often constrained by hersocial environment—in particular male mating tactics andfemalefemale competition. Males exhibit preferences for high-ranking females. In severalspecies, high-ranking females produce more offspring than low-rankingfemales. In addition, females may also influence male dominancerank and in doing so reduce male-male competition and increasemale mating success.     

Parasites and Mate Choice in Gray Treefrogs, Hyla versicolor

A fundamental assumption of the Hamilton and Zuk (1982) modelof sexual selection is that parasite-free males should producemate attracting displays that are substantially more vigorousand effective than those of their parasitized counterparts.Further, the model predicts that parasite-free males shouldbe preferred as mating partners by females and, as a consequence,should have higher reproductive success than their parasitizedcompetitors. Gray treefrogs (Hyla versicolor) constitute anideal species for testing both assumptions and predictions ofthe Hamilton-Zuk model in that: (i) mate attraction by malesrequires the production of energetically costly calls and (ii)males of this species have been shown to harbor a wide rangeof helminth parasites. The present paper summarizes resultsof analyses of calling and mating behavior by male gray treefrogsin relation to their parasite infection levels. In general,these analyses revealed no consistent relationship between thenumber and kinds of parasites harbored by males and either theduration or duty-cycle (a direct measure of energetic cost)of their calls. Furthermore, males found in amplexus (i.e.,males actually selected as mating partners by females) showeda slightly higher prevalence of parasite infection (but a slightlylower intensity of infection) than did a comparable sample ofunmated males. In sum, the present study failed to support themajor within-species prediction of the Hamilton-Zuk model ofsexual selection and also calls into question one of the fundamentalassumptions of the model.     

Egg Mimics in Haplochromine Cichlids (Pisces,Perciformes) from Lake Victoria

An ecomorphological explanation is given of the anal spots of haplochromine cichlids from Lake Victoria. Anal spots are ovoid orange-yellow spots on the anal fins of these fishes. The possible roles of sexual selection and predation as determinants of the form of these spots are discussed. Evidence is given that the anal spots are egg mimics and thus examples of intra-specific mimicry. Mimicking an egg to stimulate sexually active females presumably is an important demand on the form of the anal spots. However, no positive correlation was found between anal spot size and egg size. Light intensities of the habitat of the species investigated showed a negative correlation with anal spot size. In contrast to this, egg size did not show a negative correlation with light intensities. It is suggested that, besides mimicry, at least one more demand is involved in determining spot size: that of being conspicuous. Conspicuousness is likely to have a positive impact (benefits) on courting conspecific females, but a negative one (costs) with regard to predators who hunt visually for either adults or eggs. The actual appearance of anal spots may be a compromise. This may explain the mismatch between egg size and spot size in many species. Qualitative evidence is presented that predation pressures on adult haplochromines exerted by visually hunting predators are relatively high in lighter habitats, viz. near the rocks and near the surface. An alternative hypothesis that spots in dark surroundings cannot be seen unless they are supra-normal is discussed.     

Male Mate Choice in Trichogramma Turkestanica

In most animals it is the sex that invests the most in reproduction, generally the female, that expresses mate choice. However, in numerous species, males or both males and females are choosy. We investigated mate choice in males of the egg parasitoid Trichogramma turkestanica Meyer (Hymenoptera: Trichogrammatidae). We tested the impact of age and feeding status of males on their capacity to choose between virgin or mated and kin or non-kin females. As expected, males showed no preference between kin and non-kin mates, but inseminated virgin females over mated ones. No effect of age on the level of choosiness was found, but unfed males were choosier than fed ones. This is the first study to show an effect of feeding status of males on mate choice in insect parasitoids.     

Male Mate Choice in Lemur catta

Though females are generally more selective in mate choice, males may also derive reproductive benefits from exercising mate selectivity if one or more factors limit male reproductive success and females differ in reproductive potential. I used male mating effort as a proxy for male mate choice in ring-tailed lemurs (Lemur catta). I calculated mating effort as the rate of male-male agonism during each female's estrous period 30 min before and 30 min after the first and last mountings with intromission. I collected data on 1 free-ranging Lemur catta troop during 2 consecutive breeding seasons on St. Catherines Island, USA. In both yrs, male mating effort differed significantly among troop females once I adjusted male-male agonistic rates to reflect agonistic intensity, and I corrected for the number of observed mates per female (2000: χ² = 27.43, df = 3, p < 0.0001; 2001: χ² = 21.10, df = 3, p < 0.001). Results strongly suggest male mate choice. Contrary to expectation, males did not expend the greatest mating effort for females with the highest dominance status nor the highest reproductive success. Males preferred females that either: (1) belonged to the age class in which fecundity and infant survival is the highest at this site (4–9 yrs), or 2) were older females (≥10 yrs) with high reproductive success. Female reproductive potential appears to be an important variable determining male mating effort in Lemur catta.     

Nocturnal Mate Recognition and Nest guarding by Female Convict Cichlids (Pisces,Cichlidae: Cichlasoma mgrofasciatum)

This study investigated the ability of nest-guarding convict cichlid (Cichlasoma mgrofasciatum) females to recognize their own mate and to defend their brood effectively against strangers at night. Cichlids in the laboratory bred in nesting boxes made of plexiglas. At the fry stage, various conspecific males were introduced, at night, into the nest box of brood-guarding females. Female reaction was observed with infrared equipment. If the introduced male was their own mate, females showed little reaction. If the introduced male was a stranger, females reacted by directing head shakes, tail beats, and pushes or bites at the intruder. The frequency of these acts was significantly higher in the presence of strangers than in the presence of mates; the frequency also rose significantly as the size of strangers increased. The two largest classes of strangers fought with the females. These fights included circling behaviour, but not mouth-locking. Some aspects of female behaviour suggested that mate recognition is based on short-range chemical cues and not on sound, size, or rapidly diffusing odours. Mate recognition in the nest, at night, is an example of non-visual communication in fish, and active nest defense at night shows that the convict cichlid, normally considered to be diurnal, can engage in coordinated and effective behaviour in the absence of light.     

Hybridization Promotes Evolvability in African Cichlids: Connections Between Transgressive Segregation and Phenotypic Integration

Hybridization is a potential source of novel variation through (1) transgressive segregation, and (2) changes in the patterns and strength of phenotypic integration. We investigated the capacity of hybridization to generate novel phenotypic variation in African cichlids by examining a large F2 population generated by hybridizing two Lake Malawi cichlid species with differently shaped heads. Our morphometric analysis focused on the lateral and ventral views of the head. While the lateral view exhibited marked transgressive segregation, the ventral view showed a limited ability for transgression, indicating a difference in the genetic architecture and selective history between alternate views of the head. Moreover, hybrids showed a marked reduction in integration, with a lower degree of integration observed in transgressive individuals. In all, these data offer novel insights into how hybridization can promote evolvability, and provide a possible explanation for how broad phenotypic diversity may be achieved in rapidly evolving groups.     

Schistosomiasis transmission in Lake Malawi

Schistosomiasis (bilharziasis) transmission due to Schistosoma haematobium has for many years been known to occur along protected shorelines in Lake Malawi, but the recent finding that transmission also can also occur along open shorelines with sandy sediment has had a detrimental effect on tourism to Lake Malawi. The present paper shows that transmission, as evidenced from presence of intermediate hosts, along open shorelines is occurring in the southern part of the Lake. Relatively simple precautions can be taken to ensure minimal risk of attracting schistosome infection, and the schistosomiasis risk should not deter people from visiting and diving in Lake Malawi.     

Turbidity Hampers Mate Choice in a Pipefish

European coastal waters have in recent years become more turbid as algal growth has increased, probably due to eutrophication, global warming and changes in fish communities. Turbidity reduces visibility, and such changes may in turn affect animal behaviour as well as evolutionary processes that are dependent on visual stimuli. In this study we experimentally manipulated water visibility and olfactory cues to investigate mate choice using the sex role‐reversed broad‐nosed pipefish Syngnathus typhle as our study organism. We show that males spent significantly longer time assessing females when they had access to full visual cues, compared to when visibility was reduced. Presence or absence of olfactory cues from females did not affect mate choice, suggesting that the possible use of smell could not make up for a reduction in visibility. This implies that mate choice is environmentally dependent and that an increased turbidity may affect processes of sexual selection through an impaired possibility for visually based mate choice.     

Mate Choice and the Origin of Menopause

Human menopause is an unsolved evolutionary puzzle, and relationships among the factors that produced it remain understood poorly. Classic theory, involving a one-sex (female) model of human demography, suggests that genes imparting deleterious effects on post-reproductive survival will accumulate. Thus, a ‘death barrier’ should emerge beyond the maximum age for female reproduction. Under this scenario, few women would experience menopause (decreased fertility with continued survival) because few would survive much longer than they reproduced. However, no death barrier is observed in human populations. Subsequent theoretical research has shown that two-sex models, including male fertility at older ages, avoid the death barrier. Here we use a stochastic, two-sex computational model implemented by computer simulation to show how male mating preference for younger females could lead to the accumulation of mutations deleterious to female fertility and thus produce a menopausal period. Our model requires neither the initial assumption of a decline in older female fertility nor the effects of inclusive fitness through which older, non-reproducing women assist in the reproductive efforts of younger women. Our model helps to explain why such effects, observed in many societies, may be insufficient factors in elucidating the origin of menopause.     

Repeatability of Male Mate Choice in the Mosquitofish, Gambusia holbrooki

Male mate choice has evolved in many species in which female fecundity increases with body size. In these species, males are thought to have been selected to favour mating with large females over smaller ones, thereby potentially increasing their reproductive success. While male mate choice is known to occur, it is less well studied than female mate choice and little is known about variation in mating preference among individual males. Here, we presented individual male eastern mosquitofish ( Gambusia holbrooki ) with paired females that differed in body size, and we quantified their mate preference on two consecutive days, allowing us to assess repeatability of preferences expressed. When males were allowed to view paired stimulus females, but not to acquire chemical or tactile cues from them, they exhibited a strong preference for large females over smaller ones. However, individual males were not consistent in the strength of their preference and repeatability was not significant. When individual males were allowed to fully interact with pairs of females, the males again exhibited a preference for large females over smaller ones, as revealed by a greater number of attempted copulations with large females than with smaller ones. In the latter social context, individual male preference was significantly repeatable. These results indicate that male eastern mosquitofish from our Florida study population possess, on average, a mating preference for larger females and that this preference is repeatable when males socially interact freely with females. The significant repeatability for mating preference, based on female body size, obtained for male mosquitofish in the current study is consistent with the presence of additive genetic variation for such preferences in our study population and thus with the opportunity for the further evolution of large body size in female mosquitofish through male mate choice.     

Perception and Recognition of Vocalization in Anuran Mate Choice

Vocal communications in frogs and toads have been highly diversified and become a hot topic in the fields of herpetology,ecology,and behavioral neuroscience.The...     

Cichlid-catfish mutualistic defense of young in Lake Malawi,Africa

Summary Bagrid catfish and cichlid parents engage in a mutualistic defense of their young from predators. Over 50% of the catfish broods observed contained cichlid young, primarily of three species: Crytocara pleurostigmoides, C. pictus and Rhamphocromis sp. Three catfish broods, monitored for over 50 days, had a survivorship rate 6 times greater during periods when cichlids were present than when cichlids were absent. During two and a half h of observations of catfish broods without cichlids, I observed 23 strikes by predators on catfish young. However, when cichlids were present no foraging attacks were observed upon the catfish, but 32 occurred against cichlids in two and a half hours of observations. When the catfish parents were experimently removed the cichlid young were consumed first then the catfish young. When cichlids were present the catfish young survived over 80% longer than those in broods without cichlids. It is concluded that the parental catfish increase the survival of their own young be allowing cichlids into the brood. Because of an asymmetry of costs between the two species, cichlid mothers are more likely to abandon these interspecific broods than are the catfish.