Bi-parental care in willow ptarmigan: a luxury?

Willow ptarmigan, Lagopus lagopus, usually pair monogamously and both parents invest considerable time and energy in the care of offspring. However, the species is occasionally polygynous (5–9%), and in these cases only the females care for offspring. To examine the consequences of uni-parental care for the production of offspring and the body condition of mates, either the male or the female parent was removed at the onset of incubation and at hatch. Natural removals were also observed. Lone hen willow ptarmigan (widows) defended eggs and incubated clutches successfully, whereas single parent males (widowers) did not. After hatch, widows (mates removed either at the onset of incubation or at hatch) and pairs raised equivalent numbers of chicks to fleging, but widowers (mate removed at hatch) were less successful. There were no differences between parental types in numbers of offspring returning in a subsequent season or in the mating status of offspring in the first year of return. Widows and paired hens had similar rates of survival during the breeding season, and, in subsequent years, similar return rates and mate fidelity. Willow ptarmigan, after the onset of incubation, provided more parental care than is required to produce offspring and maintain survival and body condition of their mates. Thus, these hypotheses can be eliminated as probable factors maintaining monogamy for willow ptarmigan at this site during 1981–1984. Bi-parental care in willow ptarmigan may have developed as a salvage strategy for males as a consequence of their remaining throughout incubation to guard their mates and capitalize on the potential to re-nest.     

Parental care and social mating system in the Lesser Spotted Woodpecker Dendrocopos minor

The sexes’ share in parental care and the social mating system in a marked population of the single‐brooded Lesser Spotted Woodpecker Dendrocopos minor were studied in 17 woodpecker territories in southern Sweden during 10 years. The birds showed a very strong mate fidelity between years; the divorce rate was 3.4%. In monogamous pairs, the male provided more parental care than the female. The male did most of the nest building and all incubation and brooding at night. Daytime incubation and brooding were shared equally by the sexes, and biparental care at these early breeding stages is probably necessary for successful breeding. In 42% of the nests, however, though still alive the female deserted the brood the last week of the nestling period, whereas the male invariably fed until fledging and fully compensated for the absent female. Post‐fledging care could not be quantified, but was likely shared by both parents. Females who ceased feeding at the late nestling stage resumed care after fledging. We argue that the high premium on breeding with the same mate for consecutive years and the overall lower survival of females have shaped this male‐biased organisation of parental care. In the six years with best data, most social matings were monogamous, but 8.5% of the females (N=59) exhibited simultaneous multi‐nest (classical) polyandry and 2.9% of the males (N=68) exhibited multi‐nest polygyny. Polyandrous females raised 39% more young than monogamous pairs. These females invested equal amounts of parental care at all their nests, but their investment at each nest was lower than that of monogamous females. The polyandrously mated males fully compensated for this lower female investment. Polygynous males invested mainly in their primary nest and appeared to be less successful than polyandrous females. Polyandry and polygyny occurred only when the population sex ratio was biased, and due to strong intra‐sexual competition this is likely a prerequisite for polygamous mating in Lesser Spotted Woodpeckers.     

Polygyny in the tree swallow Tachycineta bicolor: a result of the cost of searching for an unmated male

The costs imposed by parental care duties on an individual's future survival and reproduction generate conflicts because parents should attempt to minimize their investment in the present brood, and exploit the parental care of the other parent. This conflict is likely to contribute to cases of both polygamy and desertion. Here, we study the costs of polygyny in the tree swallow Tachycineta bicolor , using observations on 52 nests that were attended by polygynous males over 14 y. Both females mated to polygynous males paid reproductive costs at several stages of the nesting cycle. Clutches laid by social mates of polygynous versus monogamous males did not differ in size. However, initial brood sizes for polygynously mated females were lower because a higher proportion of their eggs failed to hatch. Likewise, fledging success was lower and nest predation rates were higher, perhaps reflecting the direct or indirect effects of reduced male attention. These results demonstrate that females pay a productivity cost when breeding with reduced male parental care. In contrast, polygynous males fledge on average more young than monogamous ones and clearly benefit from the association. We suggest that a mate-search cost is leading to the few cases of polygamous males: although females are likely evaluating males for their prospective dedication to the breeding attempt, in a short-lived bird with a short breeding season, the cost to females of searching for a more dedicated male is the risk of not breeding at all.     

Why do pied flycatcher females mate with already-mated males?

The contribution of the pied flycatcher Ficedula hypoleuca male in parental care was studied to examine why some females mate with already-mated males. No difference in feeding rate was found between older and yearling monogamous males, when comparing nests at the same time. Monogamous and primary females were helped significantly more in parental care by the male than were secondary females of polygynous males. Females could only partly compensate for the absence of a male and of nestlings were reduced in nests with low male assistance. Differences in mate and territory quality were far too slight to make it advantageous for females to choose already-mated males instead of mating with monogamous males. We suggest that males, by being polyterritorial, deceive females into accepting polygyny; and females can be deceived since they do not have time to find out the marital status of males.     

Social organization in the pheasant (Phasianus colchicus): harem formation, mate selection and the role of mate guarding

Harem formation and mate selection were studied in the pheasant in order to determine the advantages of territorial harem defence polygyny to the two sexes. We investigated the factors affecting harem size and the advantage to a female in remaining with one territorial male during breeding.
Female group size declined during late March and early April as females moved from large overlapping ranges into smaller, more widely dispersed breeding ranges. The proportion of female groups accompanied by males increased during this period.
Some males had a disproportionate share of females. Settled females were monogamous but, because a female's nest was generally outside the male's territory, her home range was larger than his territory.
Harem members were usually from the same winter group. Harem size was not related to territory quality in terms of food supply or nesting cover. Females were loyal to one male in more than one year even if his territory position changed. Older, territory-owning males had more females, both adult and immature, than males with newly-established territories. Harem size was not correlated with territory size.
We conclude that the mating system of the pheasant is based on mate guarding which protects females not only from the risk of predation or injury, but also from excessive energy expenditure incurred through being chased by other males. When escorted by a territorial male, females spent three times as much time feeding, one-fifth as much time running, and one-tenth as much time alert, as they did when not guarded.     

Cooperation and conflict among dunnocks, Prunella modularis, in a variable mating system

The mating system of a population of 90 breeding dunnocks (or hedge sparrow, Prunella modularis) included monogamy, polygyny, polyandry and polygynandry. Monogamous males guarded females during their fertile period to prevent neighbouring males from copulating. The most intense guarding occurred where two (unrelated) males shared a territory. Here, the alpha male tried to prevent the beta male from copulating with the female. Beta males were seen to copulate in only half the cases. They were more likely to succeed when the alpha male found it difficult to guard the female closely because her range was large, the vegetation was dense or there were other females breeding synchronously on the same territory. Close guarding and chasing by males reduced the female's feeding rate and was correlated with unhatched eggs in the nest. Females attempted to escape the alpha male's attentions and actively encouraged the beta male to mate. Beta males only helped to feed the young if they copulated with the female. Nestlings fed by two males and a female got more food and weighed more than those fed by just one male and a female. Indirect evidence suggested that when beta males failed to copulate, they destroyed eggs or young chicks. Females laid larger clutches when two males mated with them as opposed to one, thus adapting their clutch size to the amount of parental care they expected. The results of natural removal experiments and matched comparisons of the same female in different mating systems support these conclusions. For females, selection favours cooperative polyandry, whereas for males if favours polygyny; the variable mating system may reflect the different outcomes of this sexual conflict.     

The role of male territories in the mating system of the Yellow-shouldered Widowbird Euplectes macrourus

The territorial system and breeding biology of the Yellow-shouldered Widowbird Euplectes macrourus (Ploceidae) was investigated in western Kenya. Yellow-shouldered Widowbirds had a resource-defence polygynous mating system: males defended large (mean = 0.95 ha) territories and built the coarse framing for the nests in tall grass. Males had up to five females nesting per territory. Females provided nearly all parental care except for a territorial male seen feeding a fledgling: the first observation of paternal care in the wild for this genus. There was considerable variation in territory size, but the cause of this variation remains unknown: territory size was not related to potential indicators of territory quality, such as grass height and abundance, did not relate to male morphology (mass, size and ornament size) or territorial behaviour (boundary displays and singing) and did not affect female preferences. Although resources (territories and nests) were defended by the males, observations that males frequently fed outside their territories and formed communal roosts during the breeding season suggest that this species represents a transitional stage between typical resource-defence polygyny and lek breeding.     

Polygyny in the yellow-headed blackbird: female choice versus male competition

Several assumptions and predictions of the polygyny threshold and sexy son hypotheses, which were proposed to explain the maintenance of polygyny on the basis of female choice, were examined. An alternative neutral mate choice hypothesis in which male competition is responsible for polygyny was also examined. For the yellow-headed blackbird, Xanthocephalus xanthocephalus, neither territory nor male features affected female choice of mate or female reproductive success. In the study population, polygyny occurred because males competed to hold territories in order to gain access to females. Since females settled apparently randomly, males that were more aggreessive and were therefore able to secure large territories had larger harems. Several criteria must be met in order for the neutral mate choice hypothesis to apply. Evidence from the literature suggests that for some species the criteria are not met and polygyny occurs due to female choice. However, several studies provide evidence that the neutral mate choice hypothesis may apply in some populations.     

Male reproductive strategy and the importance of maternal status in the Antarctic fur seal Arctocephalus gazella

Abstract. Although mammalian mating systems are classically characterized in terms of male competition and polygyny, it is becoming increasingly apparent that alternative male strategies and female choice may play important roles. For example, females who mate with males from a dominant dynasty risk producing inbred offspring. Many pinnipeds are highly polygynous, but in some species alternative male strategies such as aquatic mating appear to be important, even when behavioral observations suggest strong polygyny. Here, we analyze male reproductive success in the Antarctic fur seal Arctocephalus gazella , an otariid described behaviorally as being highly polygynous, by combining a microsatellite paternity analysis spanning seven consecutive breeding seasons with detailed behavioral data on both sexes. Territorial males fathered 59% of 660 pups analyzed from our study colony. Male reproductive skew was considerable, with a quarter of all paternities assigned to just 12 top individuals on a beach where mean annual pup production was 635. Most males were successful for only a single season, but those able to return over successive years enjoyed rapidly increasing success with each additional season of tenure. We found no evidence of alternative male reproductive tactics such as aquatic or sneaky terrestrial mating. However, paternity was strongly influenced by maternal status. Females observed on the beach without a pup were significantly less likely to conceive to a sampled territorial male than equivalent females that did pup. In addition, their pups carried combinations of paternal alleles that were less likely to be found on the study beach and exhibited lower levels of shared paternity. Thus, from a territorial male's perspective, not all females offer equal opportunities for fertilization.     

Male ornamentation, timing of breeding, and cost of polygyny in the collared flycatcher

Highly ornamented males are often thought to be better ableto provide females with resources, parental assistance, or goodgenes. Individual variation in such male abilities may overridethe costs of polygyny and therefore largely explain within-populationvariation in mating patterns. We investigated the influenceof variation in male ornamentation and the environment on thecosts of polygyny for female collared flycatchers (Ficedulaalbicollis), using data from a long-term study involving 2733breeding attempts over 19 years. We show that females sufferreduced reproductive success when mated polygynously but thatthe costs of polygyny depend on an interaction between maleornamentation and timing of breeding. Among early breeders,polygynously mated females experience higher reproductive successwhen mated to less ornamented males, but among late breeders,females mated polygynously to highly ornamented males were moresuccessful. We suggest that a high effort spent on obtainingextrapair matings early in the season renders highly ornamentedmales less able to assist two females in caring for the young.Thus, a male's ability to simultaneously gain from extrapairmatings and polygyny may be limited through direct effects onfemale reproductive success. Given such limitation, extrapairmatings may be expected to be less frequent in species withbiparental care and a high level of social polygyny.     

Male versus female mate choice: sexual selection and the evolution of species recognition via reinforcement

Male mate choice, expressed through courtship preferences, sometime occurs even under the mating system of polygyny, when the operational sex ratio is skewed toward males. The conditions under which male mate choice may be expected during polygyny are not well established. Servedio and Lande (2006, Evolution 60:674-685), assuming strict polygyny where all females have equal mating success, show that when having a preference does not increase the amount of energy that a male can put into courtship, male preferences for "arbitrary" female ornaments should not be expected to evolve; direct selection acts against them because they place males that carry them into situations in which there is high competition for mates. Here I explore in detail two situations under which logic dictates that this effect may be overcome or reversed. First I determine the contributions that direct and indirect selection place on male versus female preferences for traits that increase viability, using notation that allows the exact expression of these measures of selection. I find that direct selection against male preferences still predominates in the male mate choice model, causing less evolution by male than female preferences under these conditions. Second I address whether male mate choice is likely to evolve as a mechanism of premating isolation leading to species recognition, driven by the process of reinforcement. Reinforcement is compared under male and female mate choice, using a variety of models analyzed by both analytical techniques assuming weak selection and numerical techniques under broader selective conditions. I demonstrate that although under many conditions stronger premating isolation evolves under female mate choice, reinforcement may indeed occur via male mate choice alone.     

Effects of age and experience on the responses of territorial and floater male Red‐winged Blackbirds to models of receptive females

The ability of sexually mature non‐territorial floaters to sire offspring affects the success of floating as a breeding strategy. Red‐winged Blackbirds (Agelaius phoeniceus) have second‐year (SY) and after‐second‐year (ASY) floater males, and genetic studies suggest that floaters may gain paternity. Despite these studies, we still know little about the fitness costs and benefits of floating in this species. By presenting taxidermic models of females in soliciting, precopulatory postures in territories of experienced (previously attracted at least one mate in the study area) and inexperienced (did not previously defend a territory in the study area) males, I was able to examine the copulation behavior and success of floater male Red‐winged Blackbirds as well as the effect of experience for territorial males. Floaters trespassed during 66.1% of presentations and 85.4% of trespassers were SY males. Experienced territorial males (92.5%) and neighbors (87.5%) were most successful in attempts to copulate with models, inexperienced territorial males (62.5%) and ASY floaters (50.0%) had intermediate success, and SY floaters (6.9%) were least successful. Experienced territorial males were more likely to approach models than inexperienced males, and floaters were more likely to approach models in territories of experienced than inexperienced males. These results provide further evidence that floaters trespass frequently, suggest that floaters sire offspring, and demonstrate that prior breeding experience affects the behavior and reproductive success of territorial male Red‐winged Blackbirds. Floating appears to be a conditional strategy for ASY male Red‐winged Blackbirds, but, because it is still not known if SY floaters sire offspring, these males may be trespassing to gain information or experience.     

Parental Investment and Division of Labor in the Midas Cichlid (Cichlasoma citrinellum)

The Midas cichlid (Cichlasoma citrinellum) is an aggressive, monogamous fish living in the Great Lakes of Nicaragua. Its breeding success rates are low due to intense competition for breeding sites and high levels of predation on the young. Male Midas cichlids devote a small portion of body weight to gonads and gametes compared with females. Males produce relatively small amounts of sperm perhaps because cichlid fertilization is very efficient and the male has a high certainty of paternity. While pair members invest equal amounts of time in parental care over the course of the breeding cycle, there is a clear division of labor. Males invest more in territorial protection than do females, whereas females provide more nurturance. Both parents are active over the course of the cycle but the male invests more intensely in the early stages of the cycle. About the time the eggs hatch, the burden of care shifts to the female and she continues to invest significantly more than the male over the remainder of the cycle. Females invest much more than do males when tissue investment and parental behavior are combined. Females also assume more of the burden of care as the brood matures. The male is not free to take advantage of this and leave his mate to initiate other broods because two parents are needed to defend the breeding site and brood. Monogamy with biparental care results.     

A sexual conflict in collared flycatchers,Ficedula albicollis: early male moult reduces female fitness

A sexual conflict over levels of parental care occurs in most animals with biparental care, and studies of sexual differences in levels of parental care have usually focused on its intra-annual fitness consequences. We investigated inter-annual fitness consequences of a sexual difference in timing of feather replacement (moult) in collared flycatchers (Ficedula albicollis). In this study, males overlapped reproduction and moult more often than females, they also initiated their moult at an earlier stage of breeding than females. Females mated to males with a moult-breeding overlap had significantly lowered survival chances than females mated with males initiating moult after breeding. Furthermore, females mated with moulting males risked a lowered future fecundity in terms of a delayed start to breeding in the following season. However, early moulting males achieved a similar reproductive success as males initiating moult after breeding. Likewise, male survival probability to the following breeding season did not differ between early and late moulting individuals, nor was there any evidence that males gained or lost in future mating advantages by moulting early. These results show not only that a sexual conflict over timing of moult may operate, but also that it can impose severe fitness consequences, in terms of reduced future fecundity and survival probability, upon the ''losing'' sex.     

Effect of clutch size on male egg-fanning behavior and hatching success in the goby, Eviota prasina (Klunzinger)

In fish that exhibit paternal care, the females often choose their mates on the basis of male traits that are indicative of the parental ability of the males. In a marine goby, Eviota prasina, males tend their eggs within their nests until hatching, and females prefer males that have longer dorsal fins and exhibit courtship behavior with a higher frequency as their mates. In order to clarify the relationship between these sexually selected traits and the parental ability of males of E. prasina, the factors affecting the hatching success of eggs within male nests and the male parental care behavior were examined in an aquarium experiment. Females spawned their eggs in male nests and the clutch size of females showed a high individual variation (range = 88-833 eggs). The hatching success of eggs within male nests showed a positive correlation with the time spent by males in fanning eggs and the clutch size. In contrast to the prediction, however, the hatching success did not show a significant correlation with the sexually selected traits, i.e., the male dorsal fin length and the frequency of courtship displays. Moreover, multiple regression analysis indicated that the time spent by the males in fanning was the most important factor affecting the survival rate of the eggs. The time spent by males in fanning behavior was influenced by the clutch size within their nests; the fanning behavior of males occurred with a higher frequency when they tended larger clutches. Males are required to invest a greater effort in egg-tending behavior to achieve a higher hatching success when they receive larger clutches, probably due to the greater reward for their parental behavior. Based on their mate choice, females may obtain other benefits such as high quality offspring.     

Territory Area as a Determinant of Mating Systems

Territoriality is an integral part of breeding behavior in manyanimals. Because the reproductive success of territorial malesis often limited by access to females, breeding males shouldbehave as "area maximizers" when the basis of female choiceis either the abundance of resources within the territory orterritory area per se. Being reproductively more limited byenergy, territorial females should be "energy maximizers." Aseries of simple analytical models of territory area for suchforagers is developed to explore how changes in local food productionand/or local competitor density affect both the probabilityof a territorial male securing more than one mate (polygyny)and the probability of his and his mates' reproductive successincreasing. Two cases are modeled (only males territorial vs.both sexes territorial), each for various sets of assumptionsregarding interactions between food production, feeding efficiency,and competitor density. Concurrent responses in territory area,territory food reserves, net energy gain, and time budgetingprovide testable sets of predictions for each scenario. Whereonly males are territorial (Case I), changes in food productioncan have different (indeed, opposite) effects upon an individualmale's probability of becoming polygynous, depending upon whetherthe basis of female choice is the abundance of food within theterritory or another factor positively correlated with territoryarea. Increases in competitor density usually decrease the probabilityof polygyny regardless of the basis of female choice. Whereboth sexes are territorial and territories overlap intersexually(Case II), the mating system becomes a function of the numberof female territories within each male's territory, which varieswith the ratio of male to female territory areas. In this case,the probability of polygyny occurring will increase if foodproduction for both sexes increases without concurrent increasesin competitor density, and will decrease if competitor densityfor both sexes increases without concurrent increases in feedingefficiency. Few data are presently available to test eitherthese general predictions or numerous sets of secondary predictionstabulated in the text. Available evidence is largely consistentwith the models, but mostly circumstantial. This is becausethe predictions of these and other models of territory areaare strongly assumption dependent, and few published studieshave investigated these assumptions. These analyses demonstratethat to accurately assess the mechanisms by which environmentalfactors affect territory area, and thus mating systems, testsof the underlying assumptions of models are essential.     

Costs of large communal clutches for male and female Greater Rheas Rhea americana

The breeding system of the Greater Rhea Rhea americana is almost unique among birds as it combines harem polygyny and sequential polyandry, with communal egg-laying and uniparental male care. In this species, large communal clutches (more than 30 eggs) are rare and have a lower hatching success than smaller clutches. Here we analyse the proximate causes of hatching failures and the costs of large communal clutches (and therefore the costs of extensive polygyny) for males and females. We evaluated if length of the nesting period, egg viability, egg losses during incubation and male parental activity at the nest were affected by clutch size. We also evaluated if chicks hatched from large clutches have a lower survival during the first 2 months after hatching. Large clutches had longer nesting period and lower hatching success, mainly as a result of bacterial contamination of the eggs and increased hatching asynchrony. In addition, large clutches tended to lose more eggs as a result of accidental breakage or predation. Male activity at the nest and chick survival were not related to clutch size. Low hatching success, nest predation risk and energetic costs associated with large clutches penalize females that join large harems and males that accept additional eggs into the nest.     

Mating strategies in two species of dart-poison frogs: a comparative study

Comparative field studies of species of dart-poison frogs in the genus Dendrobates were carried out to test predictions from two hypotheses that attempt to explain female-female competition for mates in species of Dendrobates with male parental care. The sex role reversal hypothesis proposes that males invest so much time and energy in parental care that receptive males are rare relative to receptive females, and females compete to find and mate with receptive males. The parental quality hypothesis proposes that females compete to monopolize the parental effort of particular males, because they potentially suffer a cost when their mates care for the offspring of other females. Comparisons between species with male parental care (Dendrobates leucomelas) and female parental care (Dendrobates histrionicus) contradicted prediction of the sex role reversal hypothesis, but were consistent with predictions of the parental quality hypothesis. Male D. histrionicus did not compete for mates more aggressively than male D. leucomelas, and male D. leucomelas were not more selective about mating than male D. histrionicus. Female D. leucomelas and D. histrionicus were both selective about mating; female D. leucomelas associated with and competed for particular males, whereas female D. histrionicus did not.     

Should advertising parental care be honest?

Species with paternal care show less exaggerated sexual ornamentation than those in which males do not care, although direct benefits from paternal care can vastly exceed the indirect benefits of mate choice. Whether condition-dependent handicaps can signal parenting ability is controversial. The good-parent process predicts the evolution of honest signals of parental investment, whereas the differential-allocation model suggests a trade-off between the attractiveness of a mate and his care-provisioning. I show that both alternatives can arise from optimal allocations to advertisement, parental investment and future reproductive value of the male, and that the male''s marginal fitness gain from multiple matings determines which option should apply. The marginal gain is diminishing if opportunities for polygyny or extra-pair copulations are limited. Advertisement is then expected to be modest and honest, indicating genetic quality and condition-dependent parental investment simultaneously. Increasing marginal gains are likely to be related to cases where genetic quality has a significant influence on offspring fitness. This alternative leads to differential allocation with stronger advertisement, more frequent extra-pair copulations, and diminished male care. Reliability is also reduced if allocation benefits have thresholds, e.g. if there is a minimum body condition required for survival, or if females use a polygyny-threshold strategy of mate choice.     

The evolution and significance of male mate choice

The distinct reproductive roles of males and females, which for many years were characterised in terms of competitive males and choosy females, have remained a central focus of sexual selection since Darwin's time. Increasing evidence now shows that males can be choosy too, even in apparently unexpected situations, such as under polygyny or in the absence of male parental care. Here, we provide a synthesis of the theory on male mate choice and examine the factors that promote or constrain its evolution. We also discuss the evolutionary significance of male mate choice and the contrasts in male versus female mate choice. We conclude that mate choice by males is potentially widespread and has a distinct role in how mating systems evolve.