Status-dependent and strategic growth adjustments in female cooperative cichlids

Male group-living cichlids show status and strategic adjustments in growth, but females appear not to show these growth adjustments. Here, an experimental study in the Lake Tanganyika cichlid Neolamprologus pulcher elaborates on these findings. Females did not show status-dependent growth: (1) Growth in females decelerated with body size but did not depend on social status (breeder or helper), and (2) female helpers did not increase their growth rate after becoming a breeder. Females showed limited evidence for strategic growth: (3) Female helpers did not significantly adjust their growth rate depending on the treatments (comparing female helpers living in groups with a small or a large breeder female); but within the small breeder female treatment, helper growth was significantly related to their body size difference (breeder size-helper size), suggesting a strong non-linear effect of size differences on female helper growth. I conclude that these female cichlids show no status-dependent growth and only strategic growth adjustments when the size difference between the helper female and her breeder female is particularly smal

Tug-of-war over reproduction in a cooperatively breeding cichlid

In group-living animals, dominants may suppress subordinate reproduction directly and indirectly, thereby skewing reproduction in their favour. In this study, we show experimentally that this ability (‘power') is influenced by resource distribution and the body size difference between unrelated dominants and subordinates in the cichlid Neolamprologus pulcher. Reproduction was strongly skewed towards the dominant female, due to these females producing more and larger clutches and those clutches surviving egg eating better than those of subordinate females, but was not so when subordinates defended a patch. If breeding shelters were provided in two patches, subordinate females were more likely to exclusively defend a patch against the dominant female and breed, compared to when the same breeding resource was provided in one patch. Relatively large subordinate females were more likely to defend a patch and reproduce. Females also directly interfered with each other's reproduction by eating the competitors' eggs, at which dominants were more successful. Although dominant females benefited from subordinate females due to alloparental care and an increase in egg mass, they also showed costs due to reduced growth in the presence of subordinates. The results support the view that the dominant's power to control subordinate reproduction determines reproductive partitioning, in agreement with the predictions from tug-of-war models of reproductive ske

Cooperative Breeding in the Lake Tanganyika Cichlid Julidochromis ornatus

Cooperative breeding has been described for several cichlids from the genus Julidochromis (Perciformes: Cichlidae) under laboratory conditions, but field evidence is scarce. Here we describe the breeding system of the cichlid Julidochromis ornatus (Boulenger) in Lake Tanganyika (Zambia). Groups defended a breeding shelter under a large flat stone. Smaller group members stayed and fed under or close to the stone, actively guarded by the larger group members. Six out of 28 groups were newly established by breeders, joined by subordinates from a large pool of independent fish (comprising 50-70% of the total population), and four groups were seen to dissolve during a total of 77 observation days. Breeding groups consisted of a large breeding male and female with zero to five smaller subordinates (average 2). Larger breeders and subordinates were found in larger groups. All group members participated in territory defence and -maintenance, but the breeders were only present at the shelter 48% of the time, in contrast to the subordinates which guarded the breeding shelter 94% of the time. Smaller group members showed submissive behaviours to larger group members. We conclude subordinates in J. ornatus are helpers, but we did not find evidence that helpers increased the group's current reproductive success. Personal observations combined with a literature review revealed at least 19 species of Lake Tanganyika cichlids show evidence of cooperative breeding, entirely confined to the substrate breeding tribe of the Lamprologini (24% of 80 species in total): 2 Chalinochromis spp., 5 Julidochromis spp., 12 Neolamprologus spp. More effort should be put into detecting cooperative breeding in American and Asian substrate breeding cichlid specie

Life history and behavioral type in the highly social cichlid Neolamprologus pulcher

Many studies have found that seemingly unconnected behaviors are correlated into behavioral syndromes. These behavioral syndromes may be the consequence of interindividual variation in life-history strategies. Only few studies have investigated the role of behavioral syndromes in cooperatively breeding species, despite the fact that one would expect particular large variation in behavior due to the wealth of life-history decisions a cooperative breeder faces. In a longitudinal study, we repeatedly tested individuals of the cooperatively breeding cichlid Neolamprologus pulcher for exploration, boldness, and aggression and tested whether these behaviors were sex specific; whether they were interrelated; and whether they were connected to growth and to 2 major life-history decisions, helping, and dispersal. In both sexes, explorative behavior was correlated over time, even though after sexual maturity males increased their exploration rate. In both sexes, exploration, boldness, and aggression correlated when mature, and in females, helping behavior was part of the syndrome. No relationships with growth were detected. Helping and dispersal were related to each other in males, whereas females hardly dispersed. We suggest that the differences in the life histories between males and females (male dispersal vs. female philopatry) lead to the differences in behavioral types observed and also to the differences in the stability of the behavioral syndromes between the sexes. The links between dispersal and helping in males and the behavioral types and helping in females highlight the necessity to study multiple traits to understand the evolution and maintenance of variation in cooperative behavio

Individual variation and prior experience affect the discrimination of a brood-parasite by its subsocial beetle host

In birds, host experience can modify response to parasites but nothing similar is known for insects. We studied two desert tenebrionid beetles, the subsocial host Parastizopus armaticeps and its obligate and ubiquitous brood-(clepto)parasite Eremostibes opacus, which mimics the host's odour spectrum. Nearly 10% of host burrows in the field (n=214) remain unparasitised even after introducing E. opacus experimentally (n=22). In discrimination tests, 7% of naive host beetles eject the parasite, showing individual variation in olfactory discrimination ability. To test for effects of prior breeding experience, naive ("first time”) or experienced ("second time”) breeders with or without prior parasite contact were confined with E. opacus at breeding onset, their behaviour recorded and parasite number counted on breeding completion. More first- than second-time breeding pairs completely excluded the parasite and second-time breeders with no prior contact with E. opacus had fewer parasites than any others. These pairs increased burrow-guarding dramatically, mostly during early reproduction, this being the best predictor of parasite number. Prolonged guarding, however, must be traded-off against other brood-care behaviours. Hence, it might pay breeding pairs to take the risk of accepting some parasites breeding within their burrow, and we expect this effect will be more pronounced if poor feeding and digging conditions are taken into account. This might explain why apparently 90% of the P. armaticeps breeding burrows in the field contain at least one parasitic E. opacu

Life history and behavioral type in the highly social cichlid Neolamprologus pulcher

Many studies have found that seemingly unconnected behaviors are correlated into behavioral syndromes. These behavioral syndromes may be the consequence of interindividual variation in life-history strategies. Only few studies have investigated the role of behavioral syndromes in cooperatively breeding species, despite the fact that one would expect particular large variation in behavior due to the wealth of life-history decisions a cooperative breeder faces. In a longitudinal study, we repeatedly tested individuals of the cooperatively breeding cichlid Neolamprologus pulcher for exploration, boldness, and aggression and tested whether these behaviors were sex specific; whether they were interrelated; and whether they were connected to growth and to 2 major life-history decisions, helping, and dispersal. In both sexes, explorative behavior was correlated over time, even though after sexual maturity males increased their exploration rate. In both sexes, exploration, boldness, and aggression correlated when mature, and in females, helping behavior was part of the syndrome. No relationships with growth were detected. Helping and dispersal were related to each other in males, whereas females hardly dispersed. We suggest that the differences in the life histories between males and females (male dispersal vs. female philopatry) lead to the differences in behavioral types observed and also to the differences in the stability of the behavioral syndromes between the sexes. The links between dispersal and helping in males and the behavioral types and helping in females highlight the necessity to study multiple traits to understand the evolution and maintenance of variation in cooperative behavior

Clutch-size adjustments and skew models: effects on reproductive partitioning and group stability

Reproductive skew theory seeks to integrate social and ecological factors thought to influence the division of reproduction among group-living animals. However, most reproductive skew models only examine interactions between individuals of the same sex. Here, we suggest that females can influence group stability and conflict among males by modifying their clutch size and may do so if they benefit from the presence of subordinate male helpers or from reduced conflict. We develop 3 models, based on concessions-based, restraint, and tug-of-war models, in which female clutch size is variable and ask when females will increase their clutch size above that which would be optimal in the absence of male-male conflict. In concessions-based and restraint models, females should increase clutch size above their optima if the benefits of staying for subordinate males are relatively low. Relatedness between males has no effect on clutch size. When females do increase clutch size, the division of reproduction between males is not influenced by relatedness and does not differ between restraint and concessions-based models. Both of these predictions are in sharp contrast to previous models. In tug-of-war models, clutch size is strongly influenced by relatedness between males, with the largest clutches, but the fewest surviving offspring, produced when males are unrelated. These 3 models demonstrate the importance of considering third-party interests in the decisions of group-living organism

Experimental evidence for helper effects in a cooperatively breeding cichlid

Neolamprologus pulcher is a cooperatively breeding cichlid fish, in which helpers stay in their natal territory and help with brood care, territory defense, and maintenance. In this study we investigated helper effects by an experimental group size reduction in the field. After this manipulation, focal helpers in reduced groups tended to feed less, and small helpers visited the breeding shelter significantly more often than same-sized helpers in control groups. No evidence was found that remaining helpers compensated for the removed helpers by increasing territory defense and maintenance behavior. Breeders, however, did show a lower defense rate, possibly caused by an increase in brood care effort. Survival of fry was significantly lower in removal than control groups, which provides the first experimental proof in a natural population of fish that brood care helpers do effectively help. The data suggest that in small, generally younger, helpers, kin selection may be an important evolutionary cause of cooperation. Large helpers, however, who are generally older and less related to the breeders than small helpers are suggested to pay to be allowed to stay in the territory by helping. All group members benefit from group augmentatio

Behavioral type and growth rate in a cichlid fish

Behavioral syndromes or animal personalities may emerge due to covariation with different life-history strategies individual animals pursue, like risk-associated feeding rates translating in different growth trajectories. However, less clear is how this might affect individuals in cooperatively breeding species, where subordinates assist dominants in raising offspring, and growth has profound life-history and social consequences. Here, we examined the effects of behavioral type on growth rates and feeding in the cooperatively breeding cichlid fish Neolamprologus pulcher, comparing growth rates of individuals settled inside a group (dominant or subordinate) or unsettled fish (aggregation) of different behavioral types (bold-shy continuum) under a feeding regime where food could not be monopolized. Controlling for other factors, we found no effect of the behavioral type on the growth rates of dominants and subordinates in either sex. In contrast, bold female aggregation fish were significantly growing faster in length compared with shy female aggregation fish, whereas no such effect was detected in male aggregation fish. These growth rate differences were largely matched by differences in feeding rates, but locomotion appeared more important in determining growth than feeding rate. Our results show that differences in social status may need to be taken into account when testing for correlations between behavioral type and growth in vertebrates, and cautions that growth adjustments may get obscured due to correlated changes in other costly behaviors, like locomotio