Polygamous Mating System Research Articles

Premating Avoidance of Inbreeding Absent in Female Guppies (Poecilia reticulata)

AbstractThe recognition and avoidance of kin during mating can be an important means of reducing the potential for inbreeding depression in offspring. We report here that premating mechanisms to avoid inbreeding, either innate or learnt through juvenile experience, are at best weak in female guppies (Poecilia reticulata). Guppies are small, ovoviviparous, neo‐tropical freshwater fish, with a polygamous mating system where males actively court females and females are selective of their mates. In a series of mate‐choice experiments, naïve, virgin females of the Quare River population in Trinidad were given a choice between a brother and a non‐sib male from the same population. Initially, females were only provided olfactory cues upon which to base their choice and then subsequently both olfactory and visual cues. Despite the females displaying mate choice, we found no evidence of them discriminating between the male types in either experiment. There was thus no indication of inbreeding avoidance, suggesting that experiences after maturation or with mature males (e.g. rare male preference), dispersal and/or post‐mating mechanisms may be evolutionarily more important avoidance mechanisms.

Paternity and mating system in wolverinesGulo gulo

Knowledge of the wolverine Gulo gulo mating system is limited. In this study, we use 20 microsatellite loci for paternity testing in 145 wolverine offspring with known mothers. Samples were collected during > 10 years in two Scandinavian populations, mainly in connection with radio-telemetry studies and as part of long-term population monitoring. In total, 51% of the offspring were assigned a father. Our results demonstrate that the wolverine exhibits a polygamous mating system as some males were shown to produce offspring with more than one female in a single year. Females often reproduced with the same male in subsequent breeding years, but sometimes changed their partner, potentially as a consequence of a change in the territory-holding male in the area. In the majority of litters, siblings were unambiguously assigned the same father, indicating that multiple paternity is rare. Of 23 breeding pairs, for which telemetry data were available, 20 had overlapping home ranges, suggesting that pair formation generally is consistent with the territories held by wolverine males and females.

Chic chicks: the evolution of chick ornamentation in rails

Competition over access to food has led to the evolution of a variety of exaggerated visual and vocal displays in altricial nestling birds. Precocial chicks that are fed by their parents also vary widely in appearance ranging from those with inconspicuous coloration to those with brightly colored bills, fleshy parts, and plumes. These ornaments are lost by the end of the period of parental dependence, suggesting they function in competition over parental care. We use a comparative approach to evaluate which ecological or life-history variables may have favored the evolution of conspicuous ornamentation in precocial chicks. We compiled data on chick morphology, ecology, and social organization of species in the Family Rallidae, a group with highly variable downy chicks. Chick ornamentation in the form of brightly colored bills, fleshy patches, or plumes is observed in 36 of 97 species for which downy chicks are described. Phylogenetic reconstructions suggest that nonornamentation is the ancestral state. Chick ornamentation has evolved multiple times within the Rallidae and is significantly associated with large clutch sizes and polygamous mating systems. Chick ornamentation was also weakly associated with adult ornamentation and adult dimorphism. We argue that these results support the hypothesis that lineages with higher levels of sibling competition are more likely to evolve ornamented chicks. Key words: chick coloration, precocial chicks, Rallidae, sibling competition, signaling. [Behav Ecol 15:946–951 (2004)]

Timing and patterns of mating in a free-ranging population of Lycosa tarantula (Araneae, Lycosidae) from central Spain

We analysed the timing and patterns of mating in a free-ranging population of the wolf spider Lycosa tarantula (Araneae, Lycosidae) in central Spain monitored during a whole reproductive period. The population showed a polygamous mating system. However, the frequency of multiple mating was relatively low. Reproductive success of males was highly skewed, as a few males monopolized most of the copulations recorded. Males matured slightly before females but male and female maturation largely overlapped. Mortality of subadult spiders was independent of their sex, and the operational sex ratio was 1:1. Early maturation of females resulted in a larger number of visiting males but not higher mating success, indicating the possibility of female mate choice in this species.

Cloacal microorganisms and mating systems of four Australian bird species

Polygamous mating systems are expected to put sexual partners at greater risk of contracting a sexually transmissible microorganism compared with monogamy. Potentially pathogenic cloacal microorganisms such as Candida albicans, Chlamydia, coliforms and non-lactose-fermenting bacteria were studied during the non-breeding and the breeding seasons in four avian host species: two polygamous (Malurus cyaneus and Sericornis frontalis) and two monogamous (Manorina melanophrys and Neochmia temporalis). The results indicate that the highly polygamous M. cyaneus harbours more coliform and non-lactose-fermenting bacteria (which can cause disease) in its cloaca than do the polyandrous S. frontalis and the monogamous M. melanophrys. In addition, we detected higher-intensity levels of the above bacteria in avian cloacae during the non-breeding season than during the breeding season. Although not significant, trends also suggest that monogamous host species are relatively less colonised by cloacal microorganisms than are polygamous host species, whereas the latter also suffer a higher degree of multiple infection than the former.

Sperm competition and small size advantage for males of the golden orb-web spider Nephila edulis

Abstract Sexual selection, through female choice and/or male–male competition, has influenced the nature and direction of sexual size dimorphism in numerous species. However, few studies have examined the influence of sperm competition on size dimorphism. The orb-web spider Nephila edulis has a polygamous mating system and extreme size dimorphism. Additionally, the frequency distribution of male body size is extremely skewed with most males being small and few large. The duration of copulation, male size and sexual cannibalism have been identified as the significant factors determining patterns of sperm precedence in spiders. In double mating trials, females were assigned to three treatments: either they mated once with both males or the first or the second male was allowed to mate twice. Paternity was strongly associated with the duration of copulation, independent of mating order. Males that were allowed to mate twice not only doubled the duration of copulation but also their paternity. Small males had a clear mating advantage, they copulated longer than large males and fertilized more eggs. Males of different sizes used different tactics to mate. Large males were more likely to mate through a hole they cut into the web, whereas small males approached the female directly. Furthermore, small males usually mated at their first attempt but large males required several attempts before mating took place. There was no obvious female reaction towards males of different sizes.

Sex differences in behaviour as an indirect consequence of mating system

A considerable literature has been devoted to documenting differences between the sexes. However, relatively little attention has hitherto been directed towards those differences that arise as an indirect consequence of mating system even though they can have profound implications for the daily lives of the animals involved. In this review we focus on differences in the non‐reproductive behaviour of fish and relate these to sexual dimorphism in size and morphology, and to variance in fitness between the sexes. In line with our expectation, differences in distributional ecology, schooling, aggression, predator avoidance and foraging are exaggerated in sexually dimorphic species and polygamous mating systems. Nonetheless, the behaviour of males and females may also differ in sexually monomorphic and monogamous species. We conclude by highlighting promising directions for further research.

Multiple mating and reproductive success of male and female apple maggot flies, Rhagoletis pomonella (Diptera: Tephritidae).

Mature male and female apple maggot flies mated frequently on a field-caged host tree during a 14-day study. Each sex averaged one mating per day (mean of 1.0 ± 0.1), but some females mated up to eight times per day and some males up to six times per day. Reproductive success was estimated based both on observed numbers of matings in the field cage and on previous work relating fecundity and fertility to female mating status. Male and female flies did not differ in mean or variance in reproductive success, indicating that this is a polygamous mating system consisting of both polygyny and polyandry. We discuss the significance of this with regard to the framework of insect mating control and frequency proposed by others. We also discuss behaviors (such as movements, agonistic encounters, occurrences on fruit, and ovipositions) that do and do not show correlations with mating success in apple maggot flies.

Modelling the relative efficacy of culling and sterilisation for controlling populations

Simple logistic models are used to investigate and compare the effects of continuous control by culling or sterilisation on population density. The models consider populations regulated by density-dependent mortality or density-dependent recruitment, with monogamous or polygamous mating systems, and with one or both sexes sterilised. For the first time, an analytical solution is presented for the effect of sterilisation on density-dependent population growth. The models suggest that the mating system has a considerable effect on the relative efficacy of sterilisation, and that previous models for sterilisation may have overestimated the impact of sterilisation by assuming idealised monogamous mating. In general, and except for populations with monogamous mating or 'harem' systems and both sexes sterilised, culling gives a more rapid reduction in density than does sterilisation. However, the long-term degree of suppression obtained with the same levels of control applied is likely to be similar. Populations with density-dependent mortality will be reduced by sterilisation more quickly than those regulated by density-dependent recruitment, and the effect on the steady-state density of a given proportion that is sterile is greater in the first case than in the second. However, the effect of a given continuous sterilisation rate (e.g. baiting effort) on density is the same in both cases. We compare our model results with those of others and question previous conclusions about the circumstances under which sterilisation is most effective.

Sexual Dimorphism in Wild Bottlenose Dolphins (Tursiops truncatus) from Sarasota, Florida

We examined sexual dimorphism in external morphometric characters from 19 male and 32 female bottlenose dolphins (Tursiops truncatus) that were physically mature. These animals are long-term residents of the coastal waters near Sarasota, Florida, and were examined as part of an ongoing capture-release project. Males were significantly larger than females in 20 of 29 measurements; only one of eight measurements of the head showed significant absolute dimorphism. Proportional dimorphism (i.e., dimorphism corrected for body size) was less pronounced; only four linear measurements and three girth measurements exhibited significant differences between sexes. In addition, scarring of the dorsal fin occurred more frequently on males than on females. The occurrence of sexual dimorphism in this population of bottlenose dolphins is consistent with the model of a polygamous mating system.

Modelling problems in conservation genetics using Drosophila: Consequences of Harems

Polygamous mating systems occur in most mammals and some birds. They are predicted to reduce effective population sizes and to increase inbreeding and loss of genetic variation. To evaluate this theory experimentally, ten replicate lines of a Harem treatment with seven females and one male and nine replicate lines of an equal sex ratio (ESR) treatment with four pairs of parents per generation were maintained for eight generations. Equalization of family sizes was used in both treatments. Loss in average gene diversity was greater in harems than ESR (0·165 v 0·063), the effective population size lower (6·6 v 13·9), and the relative reproductive fitness lower (0·21 v 0·46). Harem mating structures should be avoided or circumvented wherever possible in the management of captive populations.

Anti-predator behaviour and mating systems in waders: aggressive nest defence selects for monogamy

Data collected from the literature on anti-predator behaviour, body weight and mating systems of 90 Holarctic waders are presented. Aggressive nest defence is correlated with body weight, heavy species being more likely to attack predators than are small species. Monogamy is common among large waders. Polygamy is generally restricted to small waders, and monogamous species are significantly more aggressive than polygamous species. Presumably, a certain body size is necessary to chase away predators, and being above this threshold size, two cooperating parents guard their nest and brood more efficiently than one parent. Small birds generally do not gain the same anti-predator advantage from monogamy as large birds, and this is presumed to explain the high frequency of polygamous mating systems in small waders.

AN EXPERIMENTAL CONFIRMATION OF MORPHOLOGICAL ADAPTATION: TOE FRINGES IN THE SAND-DWELLING LIZARD UMA SCOPARIA.

Comparative studies that reveal close associations between a character and a common selective pressure (e.g., sexual dimorphism with polygamous mating systems [Campbell, 1972]; clutch size with foraging mode [Huey and Pianka, 198 1]) can provide strong evidence for their adaptive value (Clutton-Brock and Harvey, 1979; Ridley, 1983). For morphological characters, the demonstration of the performance advantage to organisms possessing the trait in question strengthens conclusions of adaptive convergence suggested by formenvironment correlations. Studies of differential performance among species varying in the expression of a character have been used to support adaptive explanations for the character's evolution (e.g., Alberch, 1981), but interspecific comparisons (e.g., Anderson and Karasov, 1981) are weaker than intraspecific ones because of possibly confounding differences in physiological or morphological features, especially if the species are not closely related. Intraspecific functional performance studies are difficult, as variation among conspecifics in the expression of a trait of purported adaptive significance is usually so slight that demonstrations of functional advantages are both difficult and rare (e.g., Herrera, 1978; Garland, 1984). Comparative studies of morphological traits suggest three main characters that affect running in lizards: relative limb proportions (Snyder, 1954, 1962; Jaksic et al., 1980; Moermond, 1979), toe pads with lamellae (Russell, 1979; Williams and Peterson, 1982), and toe fringes (Mosauer, 1932; Luke, 1986). Experimental studies of the functional significance of these characters can be difficult. The first two are complex functional units, and, as with any such morphological system, manipulations (altering limb length or removing toe pads) to demonstrate their significance in increasing locomotor performance are problematic, as it is difficult to establish appropriate controls. Numerous intraspecific studies have quantified differential running performance in lizards (e.g., Ballinger et al., 1973; Bennett, 1980; Huey, 1982; Punzo, 1982; Hertz, 1983; Huey and Hertz, 1984), but none have studied characters presumed to have evolved specifically to aid locomotion (Laerm [1973] anecdotally reported reduced locomotor effectiveness in uncontrolled fringe removal experiments with water-running Basiliscus). Laterally projecting toe fringes on sand-dwelling lizards have long been interpreted as an adaptation for running on sand (Stebbins, 1944; Norris, 1958) and are considered a classic case of convergent evolution (Mosauer, 1932; Bellairs, 1969). A comparative study shows that fringes have evolved at least 26 different times among five lizard families, being confined mainly to sand-dwelling species (Luke, 1986; they also occur in some lizards that run on water, e.g., Laerm, 1974), supporting an adaptive explanation for their evolution. In this study, I performed experimental removals of toe fringes of a sand-dwelling lizard, Uma scoparia, to assess whether they are indeed an adaptation that significantly increases locomotor performance on sand.

The Proliferation of Cryptic Species in Chrysoperla Green Lacewings through Song Divergence

Green lacewings of the economically important genus Chrysoperla produce vibratory signals with their abdomens during courtship and mating. These signals or are complex and species-specific, and must be exchanged in a reciprocal manner between the male and female of a courting pair before copulation will take place. Such a system of communication could have evolved in response to sexual selection, selection from species isolation, or both. Sexual selection requires reasonably high variance among individuals in reproductive success, manifested as a polygamous mating system. The sympatric sibling species Ch. plorabunda and Ch. downesi, taken as representative of the genus, exhibit relatively low polygamy of females but extreme polygamy of males. However, because of irreversible sperm depletion in males, effective lifetime ability to produce offspring is approximately the same in both males and females, resulting in relatively low variance in reproductive success regardless of sex. Consequently, sexual selection alone is probably insufficient to account for the evolution and differentiation of the observed songs. On the other hand, experiments testing choice by females of conspecific versus heterospecific songs and courtship partners demonstrate clearly that calls are of the utmost importance in the reproductive isolation of closely related, potentially interfertile species. Other laboratory studies reveal that the basis for call differences between species like Ch. plorabunda and Ch. downesi is polygenic yet still simple, indicating that complete reproductive isolation and hence specification in the genus need not involve much genetic change. Thus it is not entirely unexpected that in certain regions, such as the mountains of western North America and central Europe, exist several physically indistinguishable but acoustically unique song morphs of the carnea-plorabunda-downesi complex that seem to be reproductively isolated from their often sympatric relatives only by their calling behavior. I suggest here that small, chance alteration in the genes controlling call patterns can catalyze specification in such lacewings by preventing normal individuals from dueting and copulating with mutants. Sexual selection probably facilitates the process of divergence by assuring that individuals prefer partners with extreme and therefore more attractive calls. Thus, species proliferation within the complex can occur without obvious adaptive or historical cause.

Mathematical models for polygamous mating systems

In this paper, two-sex models for populations with polygamous mating systems are developed. These models depend on the mating ratio and are applicable to both polygynous and polyandrous populations. Models for the population dynamics of populations with and without competition are constructed. Also, marriage models are discussed. The models developed describe situations common to mathematical ecology and mathematical demography. All of the models developed here are based on systems of linear and nonlinear autonomous differential equations.

SEXUAL DIMORPHISM, SEXUAL SELECTION, AND ADAPTATION IN POLYGENIC CHARACTERS.

Conspicuous sexual dimorphism is a feature of many species of higher animals. The genetic basis of variation in metrical characters, including that in sexual dimorphism between families or lines, is usually polygenic (Falconer, 1960; Frankham, 1968b; Wright, 1968, 1977; Bird and Schaffer, 1972; Ehrman and Parsons, 1976). Genetic experiments on mice, birds and Drosophila flies indicate that artificial selection practiced on a character of one sex causes not only a direct response of the character in the selected sex, but also a correlated response of the homologous character, if any, in the opposite sex (Shaklee et al., 1952; Harrison, 1953; Korkman, 1957; Becker et al., 1964; Eisen and Legates, 1966; Frankham, 1968a, 1968b; Eisen and Hanrahan, 1972). Such correlated selective responses are attributable to pleiotropy (and linkage) of genes affecting the characters of both sexes, that is, correlations between the additive effects of genes as expressed in males and females. The genetic correlation between homologous characters of the sexes is often quite high (op. cit.). As will be shown, this greatly restricts the rate of evolution of sexual dimorphism relative to that for the average phenotype of the two sexes. Sexual dimorphism may result from natural and/or sexual selection. Darwin (1874, Part 2) elucidated how natural selection operating differently on males and females arises from their distinctive roles in reproduction, or from competition between the sexes for resources such as food, leading to adaptive sexual dimorphism. He also reasoned that intrasexual contests for mates and intersexual mating preferences exert sexual selection, usually on the males, producing sexual dimorphism which is maladaptive with respect to natural selection. Comparisons within and between closely related species led Darwin to conclude that adult males typically are more modified than adult females or juveniles of either sex, but that females have often acquired male characters by transference. It was difficult for Darwin to believe that sex-limitation of characters could evolve by selection, but Fisher (1958, Ch. 6) outlined how divergent selection on the two sexes could accumulate genes with different effects in males and females, causing a character at first expressed equally in both sexes to become sexually dimorphic and finally sex-limited. The strength of sexual selection is enhanced by a polygamous mating system, but the possibility of sexual selection in monogamous systems of mating exists due to male competition for early-breeding females, and mate choice exercised by these females (Darwin, 1874; Fisher, 1958; O'Donald, 1977). Systems of mating are often thought to evolve in response to ecological pressures (reviewed by Selander, 1972; Brown, 1975; Emlen and Oring, 1977), although mating preferences may be self-reinforcing (Fisher, 1958; O'Donald, 1967, 1977; Lande, unpubl.). Darwin and Fisher described qualitative methods by which an observed sexual dimorphism could be attributed mainly to either natural or sexual selection. To assign natural selection as the primary cause requires ecological observations that males and females follow different ways of life and employ the dimorphic character(s) adaptively in their distinct modes of survival or reproduction. Darwin presented several such examples, mostly among the lower classes of animals. Selander (1972) 292

Social Interactions in Flocks of Courting Wilson's Phalaropes (Phalaropus tricolor)

A remarkable diversity of mating systems and related social behavior patterns is found in the sandpiper family Scolopacidae (including the Phalaropodinae, after Jehl, 1968). Mating systems range from territorial monogamy in the Willet (Cataptrophorus semipalmatus) (Vogt 1938), possible polygyny in the Pectoral Sandpiper (Calidris melanotos) (Pitelka 1959), polyandry in the Northern Phalarope (Phalaropus lobatus) (Raner 1972; Hilden and Vuolanto 1972) to lek promiscuity in the Ruff (Philomachus pugnax) (Hogan-Warburg 1966). In such species as the Pectoral Sandpiper (Pitelka 1959) and the Whiterumped Sandpiper (Calidris fuscicollis) (Parmelee et al. 1968), males play the active role in courtship and only females incubate, whereas the reverse is true in the phalaropes (Tinbergen 1935; H6hn 1967; Bengtson 1968). Between these extremes, other species exhibit varying degrees of role-sharing by the sexes. The strategy of pair formation in a given species probably represents a series of adaptations to a set of social and environmental conditions. Holmes and Pitelka (1966) have presented an ecological classification of social systems in calidridine sandpipers based upon the relative conservatism or opportunism in the manner of environmental exploitation. Their classification attempts to explain in particular the adaptiveness of spacing patterns of individuals during pair formation and the resulting monogamous, polygamous, or promiscuous mating system. In this paper the social phases of early pair formation in Wilson's Phalarope (Phalaropus tricolor) are examined in some detail with a view to interpreting the adaptiveness of the social behavior patterns exhibited. No attempt will be made at this stage to explain the reversal of sex roles, for which this species and its congeners are well known (Bent 1927). A later paper will deal with the interactions of the sexes during the subsequent period of avoidance of conspecifics, during which time the pair bond is completed and nesting initiated. This study follows and supplements earlier investigations into the breeding biology of W lson's Phalarope, most notably those of H6hn (1967) and Johns (1969). Names of taxa follow the classification of Jehl (1968).