Male mate preference and size-assortative mating in convict cichlids: A role for female aggression?

Many monogamous species demonstrate size-assortative mating patterns within natural populations. To better understand the role of intersexual selection in this process, we examined the effect of male preference for female body size in the convict cichlid (Amatitlania siquia). We provided males with a choice between females that differed in size, relative to each other and in relation to the focal male. Based on previous work, we expected males to prefer the largest available female mates across all treatments. Surprisingly, males spent more time near the smaller of two available females, but only when the other female was larger than the male. Additionally, males spent little time with either of two potential female mates when both females were larger than the male. We hypothesized that while males might prefer the largest of available females, female behavior might limit males from acting on this preference. To test this, males were force paired with a smaller or larger female. Pair formation only occurred when the female was smaller than the male, and females that were larger than their male counterparts showed significantly more aggression when compared to smaller females. Together, these data suggest that in the absence of intrasexual competition, male mate preference for large females in convict cichlids might be limited by female aggression.

Mating patterns of female Leon Springs pupfish Cyprinodon bovinus.

In a field study of Leon Springs pupfish Cyprinodon bovinus, two questions about female promiscuity were investigated. First, were females selective in the males with whom they spawned or were they unselective, spawning randomly among males? Second, how promiscuous were the females, i.e. with how many males did they spawn? If simply spawning with many males maximized a female's reproductive success, then females might be expected to spawn randomly with as many males as possible. Alternatively, if females were selective but engaged in multiple mating, they would limit their spawning to preferred males. In the only wild population of this endangered fish, breeding males defend closely associated territories in the shallow margins of a single desert pool. No territories were observed elsewhere in the pool. Therefore, all territorial males were present simultaneously and females could survey all of them, depositing any number of eggs with one, a few or many males. Rather than spawning randomly, females surveyed many males first, visited relatively few males and ultimately spawned with a small fraction of those available males. With increasing numbers of spawns, however, females increased the number of different mates with whom they spawned. Thus, females showed a bet-hedging tactic of having a narrow mate preference while also laying eggs in the territories of other males, possibly to reduce egg predation and to avoid inbreeding.

Are conspecific and heterospecific opponents assessed similarly? A test in two species of territorial damselfish (Pomacentridae).

Aggression is often a crucial component to interference interspecific competition and yet there are few studies that examine fight behavior when the opponents are different species. To examine conspecific and heterospecific aggression, we used two species of Caribbean damselfish, the dusky (Stegastes adustus) and the longfin (S. diencaeous) with each one serving as the heterospecific opponent to the other species. Our study was confined to whether or not each species measures the body length of the other species as if it were a conspecific intruder. Body length plays an important role in fight outcome in many species of fish and we presumed that both the dusky and the longfin would use it when assessing opponents. Both the dusky and the longfin damselfish were then presented with two individuals that were either greatly different or minimally different in size. When presented with individuals that differed greatly in size, both species spent more time attacking the larger individual, irrespective of species. However, when the size difference was small, the focal dusky and the longfin responded differently; the dusky showed no preference in either conspecific or heterospecific pairs while the longfin continued to show a bias toward the slightly larger individual. Thus, while we were surprised by the species differences, both the dusky and the longfin were internally consistent in how they treated conspecific and heterospecific opponents.

The role of sex ratios and resource availability on the pre-mating behavior of a monogamous fish.

Convict cichlid fish (Archocentrus nigrofasciatus) are one of the few monogamous species where the female appears more colorful than the male. We examined whether this sexual dimorphism was reflected in a female-biased actual sex ratio (ASR) and whether convict cichlid females would exhibit behavioral traits typified in monogamous males when they possessed the extravagant colors and/or morphology. Our field observations revealed that females are marginally, but not significantly, more abundant than males but they did initiate more intersexual social interactions (i.e. approach behavior) than males. They also showed more intrasexual aggression. Furthermore, males more commonly chased females rather than vice versa. Our laboratory experiment also indicated that differences in intrasexual aggression were not related to differences in the ASR but did appear with the addition of a breeding site. Thus, while intrasexual competition was more frequently observed between females in the field it was probably related to the availability of breeding sites rather than our estimates of the ASR.

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.

Conspecific intruders influence pair formation in a monogamous fish.

In aquaria, monogamous Texas cichlid fish (Cichlasoma cyanoguttatum) formed reproductive pairs significantly more often when another conspecific male (termed 'intruder') was visible behind a plexiglass partition. Without an intruder present, males often violently attacked and injured the female. Larger females, although attacked more frequently, were less prone to severe injuries. Pairs did not form when females were larger than males, irrespective of the presence of an intruder.

Use of a variational moment method in calculating propagation constants for waveguides with an arbitrary index profile.

A variational moment method is used to calculate propagation constants of 1-D optical waveguides with an arbitrary index profile. The method is applicable to 2-D waveguides as well, and the index profiles need not be symmetric. Examples are given for the lowest-order and the next higher-order modes and are compared with exact numerical solutions.

Eye-sighting preference of normal and hemiplegic children and adults.

Monocular eye-sighting preference was examined in 32 children with hemiplegia, 51 adult-onset hemiplegic patients and 57 normal children and adults. Eye preference was compared with ear preference on dichotic listening for 25 of the hemiplegic children. No independent association could be detected between eye preference and ear preference. In both the children and adults with hemiplegia the preferred eye tended to be on the same side as the damaged hemisphere. Among the adults, this tendency was more pronounced with more extensive lesions, as manifested by aphasia and/or hemianopia. These findings are interpreted as indicating that eye-sighting preference is unrelated to unitary hemispheric dominance, and that, unlike dominance for hearing and speech, it is not irreversible after a critical period of development. A simpler explanation than incomplete hemispheric dominance is offered for the weakly positive association between mixed laterality and cerebral dysfunction.

The effects of mate separation on pair re-formation in the Texas cichlid fish (Cichlasoma cyanoguttatum ).

This study tested whether mated pairs of Texas cichlid (Cichlasoma cyanoquttatum ) would reform and continue rearing their offspring after being separated for either one, four, or ten days. All pairs successfully re-formed after one day, while only 50% re-formed after 4 days. No pair re-formed after 10 days of separation. In successfully re-formed pairs, the female was always more aggressive than her mate, irrespective of whether the female was the resident or the returning individual. Aggressiveness seemed related to the female's attempt to control the male's parental behavior. For pairs which did not re-form, the resident parent, either the male or female, violently and continously attacked the returned mate.

Female mate choice in the pupfish, Cyprinodon variegatus.

Experimental evidence suggests that female Cyprinodon variegatus do not select between competitively inferior and superior males, but rather, deposit eggs randomly and in proportion to the size of the male's territory. The females do seem to have an habitat preference and probably influence the location where males compete for territorial space.

Interrelationships of dominance and territorial behaviour in the pupfish, Cyprinodon variegatus.

Under laboratory conditions, Cyprinodon variegatus establishes either a dominance or territorial mating system. In the dominance system, one male usually has complete access to receptive females, while in the territorial system, several males have equal access. Four factors were observed to enhance a subdominant's ability to establish a territory and improve his reproductive success; increasing the number of conspecific intruders, increasing the available area, the presence of partial barrier, and the presence of a receptive female.