M. Itzkowitz

Parental division of labour and the shift from minimal to maximal role specializations: an examination using a biparental fish

In biparental species, parents often cooperate by emphasizing different parental roles. However, these parental sex differences often disappear when only one parent is present. For example, under natural conditions, the female convict cichlid fish, Archocentrus nigrofasciatus, typically remains with the offspring while the male spends most of his time patrolling the territory and chasing intruders. With the removal of the mate, either parent is capable of raising the offspring alone, and when doing so, they each perform all parental roles. We tested how the presence and absence of the mate and the presence and absence of an intruder influence parental sex-role specialization in A. nigrofasciatus. When presented with an intruder, widowed males left the offspring unattended more often and spent more time attacking the intruder compared with widowed females. For intact pairs, males showed a tendency to leave the offspring more than their mates but this sex difference was not significant. However, these paired individuals rarely left the offspring unattended. With an intruder present, paired males and females spent the least amount of time with the offspring (compared with widows and paired individuals without an intruder present), with males spending significantly more time with the intruder than females. Unlike pairs without an intruder, parents with an intruder changed roles only in support of the other parent. Thus, females rarely approached the intruder unless the male was also present and the male rarely approached the offspring without the female also being present. We speculated that the males inability to remove the intruder caused females to support the male in attacking the intruder and the male returned to the offspring and joined the female during those periods when the intruder was least threatening.

Habitat structure and reproductive success in the beaugregory damselfish

Abstract Male beaugregory damselfish ( Stegastes leucostictus Muller & Troschel) were provided with artificial breeding sites to minimize environmental variability that might influence reproductive success. Of the two types of artificial sites, males defending “open sites” had twice the reproductive success of those males defending “closed sites”. When given a choice, males preferred to defend the open sites. Males defending open sites received more eggs and also had a larger proportion survive to hatching age than those defending closed sites. Egg survival appeared dependent on clutch size; males that received large initial clutches also attracted other females to lay eggs within their sites. Small clutches disappeared before reaching hatching age. The large variability in males defending the same types of sites suggests that females were selecting mates based on male quality. However, no correlation existed between male size and reproductive success.

Aspects of the population dynamics and reproductive success in the permanently territorial beaugregory damselfish

A beaugregory damselfish (Eupomacentrus leucostictus) population in Jamaica, W.I., was censured and revealed continuous changes in numbers of individuals for all size classes. The smallest size class, juveniles, was most abundant on the loose sand substratum while adults were common only in areas with numerous pieces of small rubble. The change in habitat from juvenile to adult is attributed to both selected mortality and active movement of the juveniles. Most females and a large segment of the adult male population exhibited continuous changes in location. Females may have been continuously searching for suitable mates while mobile males were probably searching for suitable vacant areas with spawning sites. Once a male selects a spawning site, he remains highly stationary, irrespective of his subsequent reproductive success.

Heterospecific intruders, territorial defense and reproductive success in the beaugregory damselfish

Abstract A territorial defender is expected to attack an intruder based on the intruders ability to harvest the defenders crucial resources within the territory. This prediction was tested using the territorial beaugregory damselfish Stegastes leucostictus Muller & Troschel and three different species of intruders; a herbivore ( Scarus iserti Bloch), an egg predator ( Thalassoma bifasciatum Bloch), a conspecific male. The defenders attack behavior was expected to correlate with a species potential in eating the current clutch of eggs and/or influencing the total amount of eggs secured by the defender over the summer. Intruders were tested by placing individuals in clear bottles within the defenders territory. When eggs were absent, the defenders attack rate was highest against the herbivore. When guarding eggs the defender escalated its attack behavior, uniformly, against all species. The intensity of the attack was correlated to the size of his clutch only when the intruder was the egg predator. When intruders were presented in pairs, and one of the intruders was the conspecific male, the defender always positioned himself near the bottle containing the conspecific male. Only when guarding eggs did the defending male differentiate between the egg predator and the herbivore. The total number of eggs the defender secured over the summer was not significantly correlated to his aggressive level against conspecific intruders. Thus defending males appeared to use proximate cues for defense rather than the long term reproductive benefits gained from maintaining the territory.

Parental division of labor in a monogamous fish

Both parents of the monogamous Texas cichlid (Cichlasoma cyanoguttatum) participate in offspring care and territorial defense. These activities are typically synchronized, with and without intruders being present, such that only one parent is away from the offspring. During the egg and wriggler stage, the male spends more time patrolling the territory while the female devotes more time to offspring care. During the fry stage, both parents tend to remain with the offspring. Either sex can rear the offspring in the absence of the mate. With the removal of the mate, the females activities remain largely unchanged while the male (in the absence of the female) becomes female-like. It appears as if the male adjusts his responses according to the activity of the female.

Habitat selection and subsequent reproductive success in the beaugregory damselfish

SynopsisMale beaugregory damselfish,Stegastes leucostictus, were provided with three types of artificial breeding structures to determine if they change habitats based on past or future reproductive payoffs. All three site types quickly lured males away from their natural sites. In comparison to those living on natural sites, those using artificial sites were less likely to move to different areas and had a higher reproductive success. When given no choice, male reproductive success was correlated to structural type. A second experiment provided males with an additional structure after using the intermediate quality type for 2 months. Males would often initially use both sites but would eventually shift their spawning activity to the new site if it was of the same quality or better than the old one. However, males would not move if the new site was of inferior quality. When given a new site identical to the initial one, approximately half of the males shifted to the new site. There was no evidence that reproductive performance influenced a males decision to use a new site.

Mate switching as a function of mate quality in convict cichlids, Cichlasoma nigrofasciatum

We examined mate switching between mated pairs of monogamous convict cichlids as a function of mate quality (size). A mated pair was established in each half of a 284-litre aquarium, an opaque partition separating the two pairs. When the partition was removed, mis-assorted pairs (large males with small females competing with small males with large females) re-sorted themselves such that the larger male and the larger female paired with each other 46% of the time. In contrast, when we exposed initially assorted pairs to each other, large pairs remained intact most of the time and dominated smaller pairs. The pair containing the large male, whether re-sorted or intact, dominated over the other pair and was the only one seen to spawn. Re-sortment resulted both from a preference of males for larger females and of females for larger males, and from the ability of larger individuals to displace their smaller consexual. Small females, however, when paired with a large male, often dominated large females and prevented the large female from mating with the large male. Re-sortment was also influenced by the compatibility of large individuals in their initial pairing situation. Large individuals that had been more compatible with their initial mates were less likely to switch mates. Our results support both the better-option and the incompatibility hypotheses of mate-switching. The availability of more than one breeding site in the aquarium had no effect on the frequency of re-sortment. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

Sex Differences in the Mate Selection Process Of the Monogamous, Biparental Convict Cichlid, Archocentrus Nigrofasciatum

Compared to polygynous species, monogamous males and females are considered more similar in their mate choosiness, yet few studies have explored the mate selection process between the sexes. Here, we examined this mate selection process in the monogamous convict cichlid, Archocentrus nigrofasciatus. We presented an individual (i.e. the selector) of each sex with a choice of two alternative, visually and tactilely isolated, mates. Tanks were video taped each day until the selector fish spawned with one of the potential mates (i.e. the accepted mate). The number of visits, length of visits, and courtship interactions were recorded. Selecting females spent significantly more time with accepted versus rejected males (i.e. females expressed a time-based preference for their chosen males), but there was no significant difference in the number of visits made to either male. Selecting females did not court accepted and rejected males differently, but rejected males courted at a significantly higher rate than did accepted males. Although selecting females expressed a time-based preference for accepted males, they continued to visit and court rejected males throughout the mate choice process; thus females did not terminate their selection process until they spawned. In contrast to selecting females, selecting males did not spend a significantly different amount of time with accepted and rejected females while visiting both females equally. Furthermore, selecting males courted accepted females significantly more than they courted rejected females. Thus, males expressed their mate preferences through courtship whereas females expressed them through time spent. Males also courted more than females. Many of these sex differences curiously resemble those of a polygynous social system, which we suggest perhaps indicates polygynous ancestral origins.

The costs and benefits of territorial neighbours in a Texas pupfish (Cyprinodon bovinus)

Territorial animals often establish themselves in clusters despite the presence of suitable unoccupied habitat nearby or the costly interactions involved in settling into conjoining territories. One reason for this may be that the presence of adjacent neighbours allows residents to share the costs of defending against intruders while reaping the benefits of maintaining the territories. In the Leon Springs pupfish, Cyprinodon bovinus, we compared the territories of males defending in a cluster to males defending in dispersed localities and asked whether territory residents would be more successful with or without sharing common borders with competing neighbours. Clustered residents were subjected to more intrusions by conspecific competitors and had a substantial portion of their spawning opportunities interrupted by intruding males. In particular, neighbours caused half of the spawning interruptions observed in clustered territories; in comparison, dispersed residents were rarely interrupted during spawning sequences. However, clustered males approached and spawned with more females than dispersed males, with the consequence that the overall reproductive successes of clustered and dispersed males were similar. These results are discussed in relation to the potential habitat differences between the clustered and dispersed localities and the ideal free distribution of competitors.

Competition for breeding sites between monogamous pairs of convict cichlids (Cichlasoma nigrofasciatum) : Asymmetries in size and prior residence

When pairs of convict cichlids (Cichlasoma nigrofasciatum) were forced to compete for breeding sites, intruding pairs were not able to displace residents when the intruding pair was the same size as the resident pair. This prior resident asymmetry was over-ridden when each individual of the intruding pair was larger than its same-sex counterpart in the resident pair. When only one member of the resident pair (of either sex) was the same size as its same-sexed counterpart while its mate was smaller than its counterpart in the intruding pair, the residents were able to retain control of the breeding site. Thus, only one member of the resident pair needed to be similar in size to its same-sex counterpart for the residents to retain control. Single residents, of either sex, were either displaced by the intruding pair, or formed a pair with an intruder and then remained on the site.