Male-male Competition and Female Mate Choice through Courtship Display in the Territorial Damselfish Stegastes nigricans

Both sexes of the herbivorous damselfish Stegastes nigricans maintain individual feeding territories. These territories are distributed contiguously, forming distinct colonies. Females visit male territories to spawn, and eggs are guarded by males until hatching. Male-male competition and female mate choice were studied in two colonies of different size compositions. Only larger individuals bred in both colonies. Some males in the large colony, that were larger than the breeding males in the small colony, did not succeed in reproducing probably because of severe attacks by the larger males while courting. However, females did not choose large size among breeding males. The most important male characteristic in female choice was the frequency of courtship displays in both colonies. Females in the large colony chose males mainly on the basis of the frequency of displays conducted in the females' territories, whereas females in the small colony chose males on the basis of the frequency of displays conducted in the males' territories. This difference may be a result of the difference in colony size. The distances between females' and males' territories were much greater in the large colony, and, because females cannot see courtship displays conducted in distant male territories, males in the large colony may have had to visit female territories frequently in order to conduct courtship near the females.     

Non-breeder asymmetry in Florida Scrub Jays

Summary The data of Woolfenden and Fitzpatrick (1984) show a statistically significant asymmetry in the sex ratio of non-breeders when one of the breeders is not the non-breeder's parent. I propose that the asymmetry is attributable to a combination of two factors acting on non-breeders: the value of inheriting a territory, and incest avoidance. Although natal territories are only occasionally inherited by non-breeders, and then apparently only by males, therate of inheritance is significantly higher for parent/step-parent breeders (n=6) than when both breeders are the non-breeder's parents (n=1). An alternative hypothesis, that stepparents determine the non-breeder asymmetry by ousting potential rivals, might also explain the data, but evidence is currently lacking.     

Seasonal changes in male and female bill knob size in the mute swan Cygnus olor

Sexual selection theory predicts that sexually selected ornaments are costly to maintain and, as condition-dependent signals, are likely to vary in attractiveness with season and age. Mute swans Cygnus olor possess a black, fleshy knob at the base of the bill, which is present in both sexes. Using measures calculated from digital photographs taken over two years we monitored changes in the size of the bill knob in individual swans throughout the breeding season. Our longitudinal data show that bill knob size is highly dynamic. Relative bill knob size was larger in males than females and was consistently greater for breeding males than for non-breeders. For males, relative bill knob size peaked during cygnet hatching, when male protection of the brood is most important, and was smallest during moult. In females, breeders had larger bill knobs than non-breeders at all times apart from immediately after egg-laying and incubation, when the reverse was true, presumably reflecting the costs of reproduction. Body mass was a highly significant predictor of relative bill knob size in both sexes, as was age, with an initial increase and then later a decline in relative ornament size across the lifetime of male birds. The bill knob ornament in mute swans thus appears to be a condition-dependent, highly malleable trait. It accurately reflects the differing pressures experienced by individual birds as they progress through the breeding season, suggesting selection by both intra- and inter-sexual forces.     

Reproductive behavior of the territorial herbivoreStegastes nigricans (Pisces: Pomacentridae) in relation to colony formation

Reproductive behavior of the herbivorous damselfishStegastes nigricans was studied. Both males and females held individual feeding territories, which were distributed contiguously and formed colonies. Spawning season was from June to September. Females visited males' territories and spawned eggs on the algal nest. Males tended eggs until hatching but exhibited less care taking behavior than other damselfishes. The mating system was promiscuous in that both males and females spawn with several mates, even within a single day. However, only 1 female was accepted in the nest at a time. The restriction of the number of mates in the nest may be an adptation to prevent the sneaking which was often conducted by other males of the same colony, and may also be avoidance of disturbing the spawning female. Most spawnings were done among members of the same colony and inter-colonial spawnings were rare (27 cases of 333 spawnings observed). The results of this study suggest that colonial distribution ofS. nigricans may bring several benefits in reproduction to the colony members (e.g. easy mate findings within fellow colony members), but also seems to bring costs (e.g. restriction of number of mates).     

Conflicting Territory Use in Males and Females of a Monogamous Ungulate,the Kirk's Dikdik

In monogamous mammals it is often unclear why males do not defend larger territories to attract more than one female. I investigated the territoriality of the monogamous Kirk's dikdik, Madoqua kirki, a dwarf antelope, in which food resources increase with territory size and some males defend enough resources for more than one female. Yet, all males are paired monogamously. When males were removed from small territories, their female partners spent more time outside of their territories than females in large ones. When females were removed, their male partners almost never left. Pairs in small territories spent more time together than pairs in large ones. Paired males left mostly together with their females, apparently not on their own initiative. Presumably because females in small territories left more often, their males spent more time outside in the female's company than males in large territories. I argue that males in smaller territories can keep better track of their females and that they can effectively reduce their females' time outside. Male intrusion pressure was unrelated to territory size, but it increased in the presence of unguarded females. If large territories decrease the ability to mate guard, and if unguarded females attract competing males, then defending large territories may be uneconomical, even it they could attract more than one female. On the other hand, territories must be large enough to satisfy the requirements of a single female.     

Bigamy or monogamy with maternal egg care in the triggerfish,Sufflamen chrysopterus

Reproductive behavior and mating systems of the triggerfish,Sufflamen chrysopterus (Balistidae), were studied on the fringing reef of Sesoko Island, Okinawa. Both males and females maintained territories against consexual adults, feeding on benthic animals within their own territories. Each male territory overlapped one or two female territories, with mating occurring between the cohabitants. The monogamous males were smaller and foraged more frequently than the bigamous ones, suggesting that the former allocated more energy to growth rather than to improving reproductive success. Pair spawning occurred around sunrise, females only taking care of the demersal eggs until hatching, which occurred around sunset of the same day. On spawning days females foraged less frequently than usual, but as frequently as males. Females spawned at intervals of 5–7 days, usually shifting sites within their territories. Thus both feeding and spawning sites were available for females within their territories, providing males with the opportunity to monopolize females by defending their territories.     

The social and mating system of the maternal mouthbrooderTropheus moorii (Cichlidae) in Lake Tanganyika

Territorial behaviour, reproduction and migration of the epilithic algal eater,Tropheus moorii, were investigated in Lake Tanganyika, Africa. Adults of both sexes had individual feeding territories which adjointed each other. Males, who occupied higher rocks than females, usually stayed at the same sites for more than 5 months. Females left their territories to pair with males in the males’ territories. Paired females actively foraged under the protection of their mates for up to 3 weeks prior to spawning. After spawning, females usually settled in a site unoccupied by territory-holders to mouthbrood the offspring for a month. An examination of the ovaries and a removal experiment of dominant males suggest that females cannot attain fully mature ovaries in their own territories and choose males whose territories can provide enough food to satisfy their nutritive demand. The evolution of a number of local colour morphs in this fish is briefly discussed in relation to social selection.     

Mating system of the lefteye flounder,Engyprosopon grandisquama

Underwater observations were conducted on the reproductive behavior and mating system of the lefteye flounder,Engyprosopon grandisquama, off Nagashima, southwest of Kyushu Island, Japan. Two types of males were found: large males, which defended territories against other large males, and small males, which did likewise but only against smaller males. Large males established territories which encompassed or ovelapped the home ranges of 1 or 2 cohabitant females. Territories of the small males, in which a smaller female often maintained a home range, overlapped those of large males. Pair spawning occurred around sunset. Mating of large males with cohabitant females was observed 36 times and that of a small male with a smaller female once. Pair formation was assorted by body size, paired males being larger than females in most cases. Thus, inE. grandisquama, gigamous large males were common, small males occurring within the former's erritorial boundaries mating with smaller females.     

Philopatry,morphological divergence,and kin groups: structuring in thick‐billed murres Uria lomvia within a colony in Arctic Canada

Many seabirds exhibit high natal philopatry despite their extreme dispersal ability and delayed reproduction, and some exhibit phenotypic clustering in colonies and fostering or adoption of neighbouring chicks. Previous investigations of kinship in a small thick‐billed murre colony Uria lomvia (Alcidae) in Norway revealed high relatedness among breeders on cliff ledges. To investigate the presence of kin groups and within‐colony genetic sub‐structuring elsewhere, we investigated kinship within a larger murre colony on Coats Island, Nunavut, Canada. Morphological (five characters) and genetic data (five microsatellite loci and a fragment of the mitochondrial cytochrome b gene) were analysed. Strong morphological differentiation was found among ledges. Genetic structuring was overall weak but significant at the coarse scale for males among ledges and on the east vs. the west side of the colony. Global spatial autocorrelation analyses did not detect consistent, widespread spatial patterns, although local 2D analyses provided some evidence of a tendency for larger neighbourhood sizes for females and a broad range of small to large neighbourhoods for males. Average within‐ledge relatedness was low overall, but ranged widely from slightly unrelated to greater than the level of cousins in both sexes. Kin‐level relationships occurred on ledges more frequently for same‐sex groups than expected by chance, suggesting that recruiting breeders (especially females) avoid or are unable to settle directly adjacent to relatives particularly of the opposite sex. Behavioural studies of natal dispersal of murres at Coats I. indicating that both sexes are highly philopatric, but that up to one‐fifth of females may disperse, are concordant with this study. Overall, structuring was weaker than in Norway, and may be explained in part by genetic marker and sampling artifacts, and by the lack of genetic equilibrium suspected in the much larger Canadian Arctic colony. Natal philopatry may be an important factor driving the diversification of seabirds and kin groups in other colonies and species and may be more widespread than is currently acknowledged.     

Sex-specific costs of reproduction on survival in a long-lived seabird

Costs of reproduction on survival have captured the attention of researchers since life history theory was formulated. Adults of long-lived species may increase survival by reducing their breeding effort or even skipping reproduction. In this study, we aimed to evaluate the costs of current reproduction on survival and whether skipping reproduction increases adult survival in a long-lived seabird. We used capture–mark–recapture data (1450 encounters) from two populations of Bulwer''s petrel (Bulweria bulwerii), breeding in the Azores and Canary Islands, North Atlantic Ocean. Using a multi-event model with two different breeding statuses (breeders versus non-breeders), we calculated probabilities of survival and of transitions between breeding statuses, evaluating potential differences between sexes. Females had lower survival probabilities than males, independent of their breeding status. When considering breeding status, breeding females had lower survival probabilities than non-breeding females, suggesting costs of reproduction on survival. Breeding males had higher survival probabilities than non-breeding males, suggesting that males do not incur costs of reproduction on survival and that only the highest quality males have access to breeding. The highest and the lowest probabilities of skipping reproduction were found in breeding males from the Azores and in breeding males from the Canary Islands, respectively. Intermediate values were observed in the females from both populations. This result is probably due to differences in the external factors affecting both populations, essentially predation pressure and competition. The existence of sex-specific costs of reproduction on survival in several populations of this long-lived species may have important implications for species population dynamics.     

Stress in an underground empire

The naked mole-rat (Heterocephalus glaber) and the Damaraland mole-rat (Fukomys damarensis) live in large colonies in underground tunnel systems in sub-Saharan Africa. Most members of the colonies are suppressed from reproduction and they are unlikely to reproduce during their lifetime. Only one female and a small number of males reproduce. This extreme cooperative social system has fascinated researchers since the naked mole-rat was first described as eusocial. Despite much research into the mechanisms of social suppression, the exact mechanisms are still unclear. Much evidence points towards high glucocorticoid concentrations caused by agonistic behaviour by the breeding female suppressing reproduction of non-breeders, but laboratory studies have not found any differences in glucocorticoids between breeders and non-breeders. There is, however, considerable evidence from field studies and other social mole-rats that social stress may indeed be an important factor of social suppression in social mole-rats and that those mechanisms are affected by the stability of the colony and environmental conditions. This review aims to provide a summary of the current knowledge of the relationship between environmental conditions, colony stability, glucocorticoids and reproductive suppression in social mole-rat species and suggests some avenues for future research.     

Growth and sexual strategies in the fishThalassoma duperrey (Labridae), a protogynous hermaphrodite

Synopsis Adults of the fishThalassoma duperrey, a protogynous hermaphrodite, were collected and growth observed in captivity to study the relationship between growth and reproduction among primary males, females, and secondary males. Sexual maturity is reached at about 60 mm standard length, probably less than 1 year after fertilization. Gonosomatic index in both males and females peaks at about 120 mm, nearly 2 years later. Shortly thereafter females typically change sex, and both primary and secondary males undergo color change. At the same time gonosomatic index falls abruptly and remains low in large fish. The above changes appear to reflect differences in reproductive effort over a lifetime and are interpreted as the optimum strategy given the social and mating system of this fish. Unless they cannot acquire enough food to develop large gonads, small individuals put a much greater proportion of energy into growth than reproduction apparently to minimize the period of low fitness. Intermediate-sized males and females generally invest heavily in gametes, though some retain small gonads. Large individuals (both primary and secondary males) greatly reduce their investment in gametes, probably trading the energy required to maintain reproductive territories for it. This kind of gonad ontogeny involving gonad regression, as inT. duperrey and other labrid fishes, is unique among vertebrates.     

Giant males or dwarf females: what determines the extreme sexual size dimorphism in Lamprologus callipterus?

In the Lake Tanganyika cichlid Lamprologus callipterus , males were >12 times heavier than females, the most extreme sexual size dimorphism in this direction among animals. L. callipterus males construct nests of empty snail shells in which the females breed. If the ancestors of L. callipterus were small cichlids, both sexes may have used shells for shelter. If the ancestors were larger, snail shells could not be used as shelters and would be important only for reproduction. In the field and the laboratory, females bred only in shells and the largest spawned in the largest shells. In the field, females chose larger shells than the average available in males' territories and did not copy the mate choice of other females. They never hid from predators in snail shells and they occurred commonly in areas without any potential shell shelters. In laboratory experiments females used shells only for reproduction and hardly for shelter. Therefore, it seems unlikely that L. callipterus descended from small shell-brooding cichlids which used shells for shelter, but more likely that the ancestors were of large or intermediate size, and that female size is constrained by the sizes of snail shells, which appear to be optimal breeding substrata.     

Male foraging avoidance in female feeding territories in a harem polygynous cichlid in Lake Tanganyika

We studied foraging site partitioning between the sexes in Neolamprologus tetracanthus, a shrimp-eating Tanganyikan cichlid with harem-polygyny. Females maintained small territories against heterospecific food competitors within large territories of males, foraging exclusively at the inner side of their own territories (foraging areas). Males fed as frequently as females in their own territories, but mostly outside female foraging areas, although they frequently entered female territories and repelled food competitors from the territories. Soon after removal of the resident females, however, harem males, as well as many food competitors, invaded the vacant territories and intensively devoured prey of female foraging areas. This indicates that although female foraging areas appear to contain more food than outside the areas, harem males refrained from foraging there when the resident females were present. We suggest that harem males will attempt to keep female foraging areas in good condition, whereby they may get females to reside in male territories and/or promote female gonadal maturation.     

Heterogeneity in individual quality overrides costs of reproduction in female reindeer

Reproductive allocation at one age is predicted to reduce the probability of surviving to the next year or to lead to a decrease in future reproduction. This prediction assumes that reproduction involves fitness costs. However, few empirical studies have assessed whether such costs may vary with the age at primiparity or might be overridden by heterogeneities in individual quality. We used data from 35 years’ monitoring of individually marked semi-domestic reindeer females to investigate fitness costs of reproduction. Using multi-state statistical models, we compared age-specific survival and reproduction among four reproductive states (never reproduced, experienced non-breeders, reproduced but did not wean offspring, and reproduced and weaned offspring) and among contrasted age at primiparity. We assessed whether reproductive costs occurred, resulting in a trade-off between current reproduction and future reproduction or survival, and whether early maturation was costly or rather reflected differences in individual quality of survival and reproduction capabilities. We did not find any evidence for fitness costs of reproduction in female reindeer. We found no cost of gestation and lactation in terms of future reproduction and survival. Conversely, successful breeders had higher survival and subsequent reproductive success than experienced non-breeders and unsuccessful breeders, independently of the age at primiparity. Moreover, it was beneficial to mature earlier, especially for females that successfully weaned their first offspring. Successful females at early primiparity remained successful throughout their life, clearly supporting the existence of marked among-female differences in quality. The weaning success peaked for multiparous females and was lower for first-time breeders, indicating a positive effect of experience on reproductive performance. Our findings emphasize an overwhelming importance of individual quality and experience to account for observed variation in survival and reproductive patterns of female reindeer that override trade-offs between current reproduction and future performance, at least in the absence of harsh winters.     

Hormonal and behavioural correlates of male dominance and reproductive status in captive colonies of the naked mole-rat,Heterocephalus glaber.

Naked mole-rat colonies are societies with a high reproductive skew, breeding being restricted to one dominant female (the ''queen'') and 1-3 males. Other colony members of both sexes are reproductively suppressed. Experimental removal of breeding males allowed us to investigate the relationship between urinary testosterone and cortisol, dominance rank, and male reproductive status. Dominance rank was strongly correlated with body weight, age, and urinary testosterone titres in males. No relationship between urinary cortisol levels and male reproductive status or dominance was found. Breeding males were among the highest-ranking, heaviest and oldest males in their respective colonies, and were succeeded by other high-ranking, large, old colony males. In contrast to females, no evidence of competition over breeding status was observed among males. Male-male agonism was low both before and after removal of breeders and mate guarding was not observed. The lower reproductive skew for males compared with female skew or queen control over male reproduction may explain why males compete less strongly than females over breeding status after removal of same-sexed breeders.     

Group structure,within-group conflict and reproductive tactics in cooperatively breeding Galápagos mockingbirds,Nesomimus parvulus

Reproductive conflict within groups can be an important feature of cooperative breeding systems, especially when more than one individual of a sex breeds within a social group. Relationships between group structure, dominance, within-group conflict and reproductive tactics of cooperatively breeding Galápagos mockingbirds were examined on Isla Genovesa. Territorial groups of 2–24 adults included up to three breeding females, with 42% of the groups containing more than one (plural groups); females in most plural groups nested separately. Territory size increased with group size, but the area available per pair in plural groups was smaller than in singular groups (groups with only one breeding pair). Most pairings were monogamous, and males usually outnumbered females; high-ranking males obtained mates more frequently than subordinate males. In 3 relatively dry years, but not in a wet El Niño year, subordinate pairs in plural groups fledged fewer young than dominant pairs or pairs breeding in singular groups. Interference by dominant breeders, often leading to abandonment of nests by subordinate pairs, appears to account for these differences: through nest disruption in drier years, dominant individuals may reduce the cost of sharing their territories and increase the chances of recruiting helpers. Dominant males in plural groups may also father young through extra-pair copulations with subordinate females. Despite costs imposed by within-group conflict, subordinate breeders have higher long-term reproductive success than birds that defer breeding. Plural group structure is maintained because unpredictable climatic variation favours opportunistic breeding by subordinates.     

Protandry and postandry in two related butterflies: conflicting evidence about sex-specific trade-offs between adult size and emergence time

Natural selection acting on timing of metamorphosis can be sex-specific, resulting in differences in timing between males and females. Insects with discrete generations frequently show protandry: males usually mature before females. Both Euphydryas editha and E. aurinia butterflies followed this trend. The present study was motivated by the unusual observation of consistent postandry in addition to protandry. In a single E. editha population observed over 20 years the emergence period of males was longer than that of females, both the first and last emerging individuals being males. Variance of timing among individual E. editha larvae is imposed by spatial patchiness of the snowmelt that releases them from winter diapause. If individual larvae released late from diapause were to compensate for their lateness by shortening their development times, they would be small at maturity. If such compensation were only partial, they would be both late and small. Size and timing would become associated. If females were more prone to such partial compensation than males, the observations of postandry could be explained and the prediction made that any tendency for late individuals to be small should be stronger in females than in males. This was the case: in 1 year late males were the same size as early males, in a second year they were larger. Late females were significantly smaller than early females in both years. In E. aurinia, results were opposite both to theoretical prediction and to the observations from E. editha: although the male emergence period was longer than that of females exactly as in E. editha, late males were smaller than early ones, while late females were not small. The data from E. editha support the hypothesis of a sex-specific trade-off between size and emergence time, the data from E. aurinia do not.     

Interference of asexual and sexual reproduction in the green hydra

The green hydra, Hydra viridissima, has three sexes: hermaphrodite, male, and female. I investigated the reproductive strategies of the green hydra and the relationship between asexual budding and sexual reproduction. The proportion of mature individuals in the asexually reproducing population increased with increasing temperature. Sexual reproduction did not interrupt asexual budding in hermaphrodites or males; sexual reproduction did interrupt asexual budding in females. Sexual reproduction also resulted in exponential population growth during the reproductive season. The number of asexual buds on each parental individual was positively correlated with the parental individual size in asexual individuals and in males. The same positive correlation was found between the number of testicles and the size of males. These correlations reflect a common tendency in asexual and sexual reproduction: larger parental individuals have a greater number of propagules or gametes. No correlation was found between size and buds or size and gonads in hermaphrodites; hermaphrodites had at most one asexual bud and were significantly larger than males, females, and asexual individuals. The larger size of hermaphrodites supports the hypothesis that producing both female and male gonads is more energetically costly than producing only one type of gamete (gonochorism).     

Spawning behavior and haremic mating system in the corallivorous butterflyfish,Chaetodon trifascialis, at Kuroshima Island, Okinawa

Territorial and spawning behavior ofChaetodon trifascialis were investigated on a small patch of reef at Kuroshima Island, Okinawa, Japan. Three males and 8 females inhabited the reef, each individual defending a territory against conspecifics of the same sex. Each male territory included 2 or 3 female territories. In the daytime, each male frequently visited the females living in its territory. At dusk in the full or new moon periods, courtship began within the female territories, pair spawning subsequently occurring within or near those territories. When a male actively courted a female in the territory of a second male, the latter male immediately chased off the intruder. Thus, mating occurred only between a male and females living in former's territory. This is the first report of a haremic mating system among butterflyfishes (Chaetodontidae).