Behavior and physiology of coexistence in two species of Dascyllus (Pomacentridae,Teleostei)

Synopsis In the Gulf of Aqaba Dascyllus aruanus and D. marginatus, form distinct populations organised into harems of single males and groups of females, living permanently in Stylophora and Acropora corals. Each harem consists of 4 sexual casts: dominating males, adult females, sex-changing fish and juveniles. The sexual performance of each adult fish in such social units is controlled by the presence or absence of a dominating male. In corals occupied by mixed groups of both species, only those females spawn that belong to the same species as the dominating male. Direct observation in the sea shows that such situations are produced by indiscriminative settling mechanisms of groups of juvenile fish. Evidence is also presented, demonstrating that dispersion of coral colonies suitable for occupancy and predation by piscivorous fish can modulate such complicated reproduction.     

Both-ways sex change in monogamous coral gobies, Gobiodon spp.

Synopsis We confirmed both-ways sex change in the coral-dwelling gobies Gobiodon micropus, G. oculolineatus, G. quinquestrigatus and G. rivulatus rivulatus by mate-removal experiment in the field and by the aquarium experiment of keeping two consexual fish in a coral. Eight species of Gobiodon were found in Acropora corals on the reef flat of Sesoko Island, Okinawa, southern Japan. The 4 species mentioned above bred in monogamous pairs composed of a male and a female matched by size, and the male took care of eggs deposited on the coral branch. In G. quinquestrigatus and G. rivulatus rivulatus males were larger than females in newly formed pairs, and females grew faster than their mates until breeding. The growth-rate advantage in females seems to be the major factor in the evolution of female to male sex change. The gobies strongly depended on host corals, but they moved between the corals after mate loss or coral death to form new pairs. This provides opportunities for the evolution of male to female sex change; the ability to change sex in both directions reduces the frequency of risky movement between host corals to form new pairs. These conditions are very similar to those reported in the both-ways sex change of another coral-dwelling goby Paragobiodon echinocephalus.     

Pelagic spawning of the hawkfish Oxycirrhites typus (Cirrhitidae)

Synopsis Pelagic spawning of the deep slope coral-dwelling cirrhitid Oxycirrhites typus was observed for two social groups at Papua New Guinea. This species was previously reported to be a demersal spawner in an aquarium. Courtship in social groups consisting of a single male and one or two females commenced just prior to or after sunset among the branches of gorgonian or antipatharian corals. Males and females occupied separate corals; males either visited females at their corals or met them at an adjacent coral just prior to courtship. Courtship was sequential and consisted of two or more bouts with each female that culminated in a rapid ascent into the water column and the release of floating eggs. Fertilized eggs, taken from a third social group, were spherical and averaged 0.69 mm in diameter. Spawning pairs sought refuge in their resident corals or in the coral where courtship occurred immediately after spawning was completed.     

The Relationship Between Resource Control, Association with Females and Male Weapon Size in a Male Dominance Insect

In species with a resource‐defence (male dominance) mating system, males are expected to maximize fitness by controlling resources deemed more valuable by sexually receptive females because these sites attract more mates. Furthermore, males, which control more valuable resources should themselves be of high quality. I experimentally tested these predictions in the laboratory using the sexually dimorphic Wellington tree weta, Hemideina crassidens (Blanchard) (Orthoptera: Tettigonioidea: Anostostomatidae). Male H. crassidens use their mandibular weaponry to fight for control of harems (groups of adult females) that seek shelter in trees cavities (galleries). As predicted, larger galleries housed significantly larger groups of females and males with larger weaponry controlled large galleries significantly more often. Therefore, galleries with a larger volume are likely considered more valuable by males because they house larger harems. However, contrary to prediction, males with larger weaponry did not reside with significantly more females overall because females did not always form the largest possible groups in galleries and males with smaller weaponry were able to reside with single females in small galleries. The latter observation suggests a possible alternative mating strategy by disadvantaged males.     

Harem size and oviposition behaviour in a polygynous bark beetle

Abstract. 1. Harem polygyny can have fitness benefits and costs on females. In bark beetles of the genus Ips the latter may include within‐harem competition between larvae. However, earlier competition between females for male care and mating opportunities may also influence oviposition behaviour. There has been relatively little investigation into the relationship between harem size and initial egg output. The present study investigated this relationship in the bark beetle Ips grandicollis. 2. The measure of egg output used was the number of eggs in the gallery with the most eggs in each harem. Mean (±SE) harem size of 242 observed harems was 3.25 ± 0.10. A curvilinear relationship was found between egg output and harem size, with females in smaller harems (one to four females) laying more eggs with increased harem size. However, females in larger harems (five to seven females) laid fewer eggs as harem size increased. The optimal harem size (in terms of number of eggs laid) was close to four females. 3. We found no evidence from a behavioural assay that females could preferentially choose unmated males over mated males with harems of two females. Additionally, the distribution of harem sizes suggests that females distribute themselves among males randomly. 4. The results suggest that harem size has effects on female reproduction that extend beyond larval competition and influence patterns of oviposition. The mechanism that determines why egg laying is greatest at intermediate levels is unknown. There is no evidence that smaller harems belong to lower quality males, but females may adjust egg‐laying behaviour in large harems as a result of reduced male attendance or anticipated larval competition.     

Individual variation in perfume blending in male greater sac-winged bats

Male greater sac-winged bats, Saccopteryx bilineata, use hovering flights to court females in their harem territory. While hovering, males fan a fragrant perfume from sac-like organs in the wing membrane towards the females. Each afternoon, males renew the perfumes of their wing sacs during a stereotypical and time-consuming behavioural sequence, which includes blending secretions from genital and gular glands. I investigated whether male perfume-blending behaviour varies between the mating and the nonmating season, and whether successful males, those with large harems, have different patterns of perfume blending than less successful males. I measured variation in perfume-blending behaviour in 21 adult males. The pattern of perfume blending was not significantly different between the mating and the nonmating season. However, the time at which perfume blending began and terminated differed between seasons. During the mating season, males spent about the same time cleaning their wing sacs during phase I of perfume blending, irrespective of the number of females in their harem. During phase II, males with large harems spent significantly less time refilling and blending perfume than males with small harems. In addition, males with large harems took up fewer droplets of secretion from the genital region. Overall, male-male interactions were rare during perfume blending, and the decrease in duration in phase II was not attributable to more disturbance in large harems. There was also no evidence that males prevented each other from transferring secretions into their wing sacs. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Grooming and group structure in hamadryas baboons

The results of 3-year observation on coral living hamadryas baboons transported from natural habitat in Tuapse reservation have been presented. Despite of the fact that grooming between males and females accounted for 73% of total cases of grooming in adult individual pairs, only the relationships of males with high-ranked females of their harems fully corresponded to a star-shaped sociogram. The high-ranked females were not different from all the other females either according to a total number of grooming cases with their female partners or according to a proportion of a performed and received grooming. Grooming between the related females was noted predominantly in the cases when they belonged to the same harem. Grooming between the related males accounted for 59% of all the cases of grooming between the male partners.     

The influence of colony size and coral health on the occupation of coral-associated gobies (Pisces: Gobiidae)

Fishes of the genus Gobiodon are habitat specialists by their association with Acropora corals. Little is known about the parameters that define host coral quality for these fishes, in particular their breeding pairs. Data were collected in the northern Red Sea using 10 × 1-m belt transects in different reefs and zones. Gobiid density was highly correlated with coral density over all sites and zones, and the more specialized goby species preferred coral species that are less vulnerable to environmental stress. Moreover, the occupation rate of corals by goby breeding pairs significantly increased with colony size and decreased with partial mortality of colonies. Logistic regression showed that both coral size (being most important) and partial mortality are key factors influencing the occupation by breeding pairs. This study provides the first evidence that breeding pairs of coral-associated gobiids have more advanced habitat requirements than con-specifics in other social states. As coral reefs are threatened worldwide and habitat loss and degradation increase, this information will help predict the potential effects on those reef fishes obligatorily associated with live corals.     

Why do male chimpanzees defend a group range?

Male chimpanzees, Pan troglodytes, cooperate to defend a community range within which resident females range in smaller core areas. There has been debate over exactly what males are defending, whether mates, territory or both. One hypothesis holds that males are defending mates, and that an increase in community range size will lead directly to the acquisition of more females. However, males frequently attack females as well as males at the edge of the community range. We examined 18 years of observational data on the Gombe chimpanzees to determine the behaviour of males during extragroup encounters, and the consequences of changes in community range size on the number of adult females and indirect measures of food availability. Males were always aggressive to males from other communities, and often attacked adult females, especially those that were not sexually receptive, were older, and/or had more than one offspring. The number of females did not increase with range size, but several measures suggested an increase in food availability with range size. These measures include more time spent in large foraging parties, higher encounter rates with resident females, more encounters with sexually receptive females and higher female reproductive rates. These findings suggest that males defend a feeding territory for their resident females and protect them from sexual harassment. Although a large range may eventually attract more females, this is not an immediate consequence of range expansion. Male number was not correlated with community range size.     

Subordinate Males in Harem Groups of Jamaican Fruit‐Eating Bats (Artibeus jamaicensis): Satellites or Sneaks?

In the caves of Yucatan, Mexico, the Jamaican fruit‐eating bat, Artibeus jamaicensis, forms harems consisting of four to 18 females and a dominant male that defends the group against foreign males. Large groups (>14 females) contain an additional subordinate male. In theory, subordinate males can associate with harem groups either as satellites, if they provide at least some benefits to the dominant male, or as sneaks, if they only impose costs on the dominant male. We assessed the costs and benefits of subordinate males in three removal experiments. In the first experiment, when a dominant male was removed from its group, its role was occupied by the subordinate male (in large groups) or by a foreign male (in small groups). Former subordinate males took less time to gain control of the harems and stayed longer with the groups than foreign males. In the second experiment, when a subordinate male was removed, the rate of visitation by foreign males and the number of agonistic displays by the dominant male both increased. In the third experiment, when the number of females in large groups was reduced, subordinate males spent less time with their groups and the rate of visitation by foreign males increased. However, the frequency of agonistic displays by dominant males towards subordinate males did not change. Dominant males invest large amounts of energy in defending the harems, but obtain direct and immediate benefits from the presence of subordinate males in the form of access to a larger number of females, and suffer no obvious costs. Subordinate males apparently invest little energy in defending the harems, obtain no obvious immediate benefit, but gain long‐term benefits by having priority access to vacant positions left by dominant males. Subordinate males in harem groups of the Jamaican fruit‐eating bat can be considered satellites because their presence brings immediate benefits to the dominant males.     

Social Organisation of the Bat Tadarida (Chaerephon) pumila (Chiroptera: Molossidae) in Ghana,West Africa

The social organisation of the polyoestrous bat, Tadarida pumila, was studied in northern Ghana (W. Africa). Although this small (8.5 g) free-tailed bat is not sexually dimorphic in size, adult males develop an odorous inter-aural crest of long hairs. A social system based on female defense polygyny was found which, however, also involved elements of resource defense. Harems, each generally established in the roof space of separate dwelling houses with restricted access, consisted of an adult male and up to 21 females, with their young, and the larger harems were held by heavier males. Harem composition was stable and both harem males and females showed high site fidelity over the study span of 16 months. Some female young were recruited to their natal harems, at a sufficient rate to replace the annual loss of harem females. However, most young, which were born in three successive cohorts during the rainy season, apparently dispersed over the dry season, following early sexual maturation. The potential causes and benefits of female associations are discussed.     

Effects of size and sex on the social organization of reef-associated hogfishes,Bodianus spp.

Synopsis Three species of wrasses (Labridae) were examined in the field to determine the relative importance of size and sex in structuring social organization. The Spanish hogfish, Bodianus rufus, was characterized by stable dominance hierarchies that were linearly organized according to sex and relative size. Males were the largest and most-dominant individuals within discrete social groups of females (harems) whose dominance increased with body size. Dominance rank also increased with body size among both males and females of the Mexican hogfish, B. diplotaenia. Most encounters occurred between the sexes and males were clearly dominant over females. The vieja, B. eclancheri, differed from the other congeners since social interactions were not strongly patterned by either relative body size or sex. Hogfish dominance relationships appear to develop according to the manner in which males compete for females, including the formation of harems in permanent territories with single-male pairspawns (B. rufus), defense of temporary reproductive territories with single-male pairspawns (B. diplotaenia) or maximizing sperm production in multi-male group spawns (B. eclancheri).     

Pairs and Harems in a Cichlid Fish,Lamprologus brichardi1

L. brichardi is a substrate brooding cichlid with facultative polygamy. The social organization was studied in the field for a 6-week period. The mating structure was examined in detail in the laboratory. Two types of social groupings are described:

• 1 Aggregations of sexually mature but nonterritorial fish, also frequently visited by territory holders in the vicinity.
• 2 Reproductive units (families) mainly consisting of the reproducing pair members and offspring from several broods. All family members defend a common territory around the shelter site. Occasionally a male has access to two females each with a separate territory (harem).

The factors influencing mating structure were investigated in the laboratory:

• 1 Females select breeding sites rather than partners.
• 2 Without competitors for breeding sites, and with an equal or nearly equal sex ratio, harems were established nearly as often as pairs.
• 3 Young males are physically able to mate and form a harem; but they are usually prevented from doing so by more competitive (larger) males.
• 4 Competition for breeding sites is not a prime influence on harem formation, although it is of great importance in determining the composition and size of the breeding population.
• 5 Just as many pairs as harems were formed with and without predators, even though, with predators, no young survived.
• 6 In L. brichardi the formation of harems is not predominantly determined by the distribution of suitable spawning sites. The monopolization of females is only slightly influenced by the distance between their territories.
• 7 In L. brichardi it is not necessary for harem formation that the male is bigger than the female.
• 8 Behavioural protocols and data on growth rates, as well as spawning intervals, did reveal any consistent difference between pairs and harmes.

Of the variables tested, male competition for females was therefore the sole determinant of who should mate.     

The Association of Two Gall Crabs (Brachyura: Cryptochiridae) with the Reef-building Coral Siderastrea stellata Verrill, 1868

The family Cryptochiridae includes a small group of cryptic crabs that inhabit cavities in scleractinian corals. They are represented in Brazil by two species. Troglocarcinus corallicola, found from Maranhão to Bahia states and that occurs in many species of the coral families Mussidae, Faviidae, Caryophillidae and Siderastreidae. Opecarcinus hypostegus, reported from the state of Pernambuco, is mainly associated with Agaricia fragilis. The range of O. hypostegus is extended to Rio Grande do Norte and Alagoas states. Males are usually smaller than females, and couples may be eventually found sharing cavities. Ovigerous females and males of O. hypostegus are recorded for the first time inhabiting adjoining cavities on colonies of Siderastrea stellata, an endemic reef coral widespread along the Brazilian littoral.     

Spatial Variation in Abundance,Size and Orientation of Juvenile Corals Related to the Biomass of Parrotfishes on the Great Barrier Reef,Australia

For species with complex life histories such as scleractinian corals, processes occurring early in life can greatly influence the number of individuals entering the adult population. A plethora of studies have examined settlement patterns of coral larvae, mostly on artificial substrata, and the composition of adult corals across multiple spatial and temporal scales. However, relatively few studies have examined the spatial distribution of small (≤50 mm diameter) sexually immature corals on natural reef substrata. We, therefore, quantified the variation in the abundance, composition and size of juvenile corals (≤50 mm diameter) among 27 sites, nine reefs, and three latitudes spanning over 1000 km on Australia’s Great Barrier Reef. Overall, 2801 juveniles were recorded with a mean density of 6.9 (±0.3 SE) ind.m⁻², with Acropora, Pocillopora, and Porites accounting for 84.1% of all juvenile corals surveyed. Size-class structure, orientation on the substrate and taxonomic composition of juvenile corals varied significantly among latitudinal sectors. The abundance of juvenile corals varied both within (6–13 ind.m⁻²) and among reefs (2.8–11.1 ind.m⁻²) but was fairly similar among latitudes (6.1–8.2 ind.m⁻²), despite marked latitudinal variation in larval supply and settlement rates previously found at this scale. Furthermore, the density of juvenile corals was negatively correlated with the biomass of scraping and excavating parrotfishes across all sites, revealing a potentially important role of parrotfishes in determining distribution patterns of juvenile corals on the Great Barrier Reef. While numerous studies have advocated the importance of parrotfishes for clearing space on the substrate to facilitate coral settlement, our results suggest that at high biomass they may have a detrimental effect on juvenile coral assemblages. There is, however, a clear need to directly quantify rates of mortality and growth of juvenile corals to understand the relative importance of these mechanisms in shaping juvenile, and consequently adult, coral assemblages.     

Alternative spawning tactics of female angelfish according to two different contexts of sex change

Social conditions for sex change and reproductive success werestudied in the haremic marine angelfish, Centropyge ferrugatus,in the coral reefs of southern Japan. In this species the largestfemale in a harem changed sex not only after disappearance ofthe dominant male but also occasionally in his presence. Inisolated harems containing two to three females, strict socialcontrol by the dominant male resulted in females changing sexonly after the male disappeared (takeover sex change). In haremsadjacent to each other, however, takeover sex change did notoccur even when one of the males disappeared. Instead, largeharems including more than four females were formed by fusionof two adjacent harems. In such large harems, the dominant malewas unable to socially prevent the largest female from changingsex later to acquire a portion of the harem (harem-fission sexchange). Females in adjacent harems spawned less frequentlyand tended to grow faster than those in isolated harems, probablyto gain an advantage in dominance status over neighbors of similarsize. Thus, females changed spawning frequencies according tothe two different contexts of sex change. The takeover tacticresults in higher fitness than the harem-fission tactic, whichshould be the best in the bad situation of adjacent harems.     

Experimental tests of copying and mate choice in fallow deer (Dama dama)

In fallow deer (Dama dama), as well as in other lek-breedingungulates, receptive females arriving at leks commonly joinmales that are defending large harems. This tendency enhancesdifferences in harem size and mating success between males.It could occur because females independendy move to the samemales, because females are attracted to males with females,or because females are attracted to each other. Using controlledexperiments with estrous female fallow deer, we show that, althoughfemales are more attracted to males with harems than to thosewithout, they are as frequently attracted to groups of femaleswithout a male as to female groups with males. We conclude thatfemale fallow deer joining leks are attracted to each otherand copy each other's movements. As yet, there is no firm evidencein fallow deer or in other lek-breeding ungulates that femalescopy each other's choice of mating partners. Key words: Damadama, fallow deer, lek breeding, mate choice, copying behavior.[Behav Ecol 4: 191–193 (1993)]     

Defence of Females by Dominant Males of Artibeus jamaicensis (Chiroptera: Phyllostomidae)

Defence of females by dominant males of the Jamaican fruit‐eating bat Artibeus jamaicensis was observed in two natural colonies over 2 yr. A log‐linear model was used to evaluate the frequency distribution of visits to harems by sex, season and agonistic interaction of dominant males. Harem group size varied from four to 18 females, with one adult male in the small and medium‐sized groups and two males in the large groups (> 14 females). A highly significant interaction was noted between the age and sex of the visitor and the response of the dominant male. Male visitors were attacked more often than female and juvenile visitors. Aggressive defence increased during the reproductive seasons, with dominant males showing more agonistic responses towards male visitors. An increase in the frequency of visits by male visitors was noted in harem groups that ranged in size from four to 12 females, but the frequency of male visits declined in harem groups that contained more than 14 females.     

Effect of habitat characteristics on the distribution and abundance of damselfish within a Red Sea reef

For coral reef fish with an obligate relationship to their habitat, like Pomacentrid damselfish, choosing a suitable home amongst the reef structure is key to survival. A surprisingly small number of studies have examined patterns in adult damselfish distributions compared to other ontogenetic phases. The aim of this study was to determine which reef and coral colony characteristics explained adult damselfish distribution patterns in a Red Sea reef. The characteristics investigated were reef type (continuous or patchy), coral species (seven species of Acropora), and coral morphology (coral size and branching density). The focal damselfish species were Dascyllus aruanus, D. marginatus, Chromis viridis, and C. flavaxilla. Occupancy (presence or absence of resident damselfish), group size and fish species richness were not significantly different between the seven Acropora species. However, within each coral species, damselfish were more likely to occupy larger coral colonies than smaller coral colonies. Occupancy rates were also higher in patchy reef habitats than in continuous sections of the reef, probably because average coral colony size was greater in patchy reef type. Fish group size increased significantly with coral colony volume and with larger branch spacing. Multi-species groups of fish commonly occurred and were increasingly likely with reduced branching density and increased coral size.     

Closing the circle: is it feasible to rehabilitate reefs with sexually propagated corals?

Sexual propagation of corals specifically for reef rehabilitation remains largely experimental. In this study, we refined low technology culture and transplantation approaches and assessed the role of colony size and age, at time of transfer from nursery to reef, on subsequent survival. Larvae from Acropora millepora were reared from gametes and settled on engineered substrates, called coral plug-ins, that were designed to simplify transplantation to areas of degraded reef. Plug-ins, with laboratory spawned and settled coral recruits attached, were maintained in nurseries until they were at least 7 months old before being transplanted to replicate coral limestone outcrops within a marine protected area until they were 31 months old. Survival rates of transplanted corals that remained at the protected in situ nursery the longest were 3.9–5.6 times higher than corals transplanted to the reef earlier, demonstrating that an intermediate ocean nursery stage is critical in the sexual propagation of corals for reef rehabilitation. 3 years post-settlement, colonies were reproductively mature, making this one of few published studies to date to rear a broadcasting scleractinian from eggs to spawning adults. While our data show that it is technically feasible to transplant sexually propagated corals and rear them until maturity, producing a single 2.5-year-old coral on the reef cost at least US$60. ‘What if’ scenarios indicate that the cost per transplantable coral could be reduced by almost 80 %, nevertheless, it is likely that the high cost per coral using sexual propagation methods would constrain delivery of new corals to relatively small scales in many countries with coral reefs.