Group Size and Direct Fitness in Social Queues

Shreeves, Gavin; Field, Jeremy

doi:10.1086/324125

Cited by 73 publications

(52 citation statements)

References 45 publications

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“…Evidence that helpers can have short-term effects on offspring fitness by increasing juvenile survival has previously been shown, for example through removal experiments in several cooperatively breeding species [35]–[37], [71]. However whether helping has long-term fitness benefits has long remained unclear, reflecting the fact that helper effects are hard to study, not only because long-term data are needed, but also since specific approaches (e.g.…”

Section: Discussionmentioning

confidence: 99%

Helpers at the Nest Improve Late-Life Offspring Performance: Evidence from a Long-Term Study and a Cross-Foster Experiment

2012

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BackgroundConditions during an individual's rearing period can have far reaching consequences for its survival and reproduction later in life. Conditions typically vary due to variation in parental quality and/or the environment, but in cooperative breeders the presence of helpers adds an important component to this. Determining the causal effect of helpers on offspring fitness is difficult, since high-quality breeders or territories are likely to produce high-quality offspring, but are also more likely to have helpers because of past reproductive success. This problem is best resolved by comparing the effect of both helping and non-helping subordinates on offspring fitness, however species in which both type of subordinates commonly occur are rare.Methodology/Principal FindingsWe used multi-state capture-recapture models on 20 years of data to investigate the effect of rearing conditions on survival and recruitment in the cooperatively breeding Seychelles warbler (Acrocephalus sechellensis), with both helping and non-helping subordinates. The number of helpers in the rearing territory, but not territory quality, group- or brood size, was positively associated with survival of offspring in their first year, and later in life. This was not a result of group size itself since the number of non-helpers was not associated with offspring survival. Furthermore, a nestling cross-foster experiment showed that the number of helpers on the pre-foster territory was not associated with offspring survival, indicating that offspring from territories with helpers do not differ in (genetic) quality.Conclusions/SignificanceOur results suggest that the presence of helpers not only increase survival of offspring in their first year of life, but also subsequent adult survival, and therefore have important fitness consequences later in life. This means that when calculating the fitness benefits of helping not only short-term but also the late-life benefits have to be taken into account to fully understand the evolution of cooperative breeding.

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Section: Discussionmentioning

confidence: 99%

Helpers at the Nest Improve Late-Life Offspring Performance: Evidence from a Long-Term Study and a Cross-Foster Experiment

2012

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“…Thus, the probability of inheriting the dominant's breeding status in this case may be quite high, which means that i may also be very high and that it will be very hard for the condition for caste differentiation, , to be satisfied. Yet a 1 (1 Ϫ w)i as group size increases because of various ecological pressures, the increased number of competitive subordinates decreases the probability of a particular subordinate acquiring dominant status until the condition for caste differentiation is met (Shreeves and Field 2002). Put another way, a totipotent subordinate living in a parent-offspring group where the group size has reached a certain critical point may transmit its genes more efficiently by developing into a morphological worker caste at the cost of a part of its reproductive potential than by retaining its full reproductive potential and waiting for the dominant's death.…”

Section: Integrating Group Size With Reproductive Skewmentioning

confidence: 99%

Reproductive Skew and the Origin of Sterile Castes

Jeon

Choe

2003

The American Naturalist

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Reproductive skew theory has not heretofore formally addressed one of the most important questions in evolutionary biology: How can whole-life sterile castes evolve? We construct a transactional skew model investigating under what conditions a subordinate in a multimember group is favored to develop into a morphologically specialized worker caste. Our model demonstrates that, contrary to former expectations, the ecological and genetic conditions favoring caste differentiation are far more restrictive than those favoring high skew. Caste differentiation cannot be selected in saturated, symmetrical relatedness groups unless the genetic relatedness among group members is extremely high. In contrast, it can be selected in the saturated, asymmetrical relatedness (parent-offspring) groups with complete skew. If we also consider the future reproduction of subordinates, caste differentiation is possible only after the group size reaches a certain critical point. Most importantly, caste differentiation in a parent-offspring group increases its saturated group size. The positive feedback between group size and the degree of caste differentiation can continue in principle until completely sterile worker castes emerge. Thus, at least in the case of parent-offspring groups, group size but not the degree of reproductive skew may be a better index of the level of social complexity. A scheme for the evolution of sterile worker castes that integrates the role of group size into the framework of reproductive skew theory is proposed.

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“…Staying incentives (Reeve & Keller, 2001) are one means by which dominants can induce other individuals to remain within the nest. Staying incentives ceded by dominant females may be expected in this species, given that larger colony size is likely to increase the chance that some younger females will be present to rear the offspring of older females when the latter die (Shreeves & Field, 2002). The finding that relatively large body size predicts ovary size in old females but not in young females is consistent with this expectation: older females are less likely to provide the level of ‘brood insurance’ (Field et al ., 2000) expected from young females, and therefore the staying incentives ceded to young females should not be given to older females.…”

Section: Discussionmentioning

confidence: 99%

Cooperative nesting and complex female-biased sex allocation in a tropical allodapine bee

Thompson

Schwarz

2006

Biological Journal of the Linnean Society

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Patterns of sociality and sex allocation are well known for many allodapine bee genera, but have only been described for one species in the genus Macrogalea . Macrogalea is the sister group to the remaining allodapines and is important for inferring plesiomorphic features for the tribe. The present study describes the broad elements of social behaviour and the patterns of sex allocation in an undescribed Macrogalea species from Malawi, and provides the most detailed description of sociality and sex allocation in this genus. This species has large maximum colony sizes (13 adult females) compared to most other allodapines and there is no evidence of reproductive castes. Alloparental care is common and probably unavoidable because brood are progressively reared in a communal burrow where parental care cannot be restricted to filial brood. Cooperative nesting confers substantial benefits in avoiding brood loss, and via enhancement of both per capita brood production and mean pupal weight, but per capita benefits decline after colony sizes exceed three females per nest and total brood size saturates once colony sizes exceed five or six females. All newly eclosed females lay eggs, regardless of body size, but reproduction by older females depends on their relative body size. This suggests the existence of staying incentives for young females, who are potentially valuable alloparents, but that there is reproductive competition among older females who would have little future value as alloparents. The sex ratios are among the most strongly female biased in any bee studied to date, with a colony mean of r ∼ 0.08. There is almost no production of males in colonies with five or fewer adult nestmates, but bias declines very rapidly once colonies exceed this size. This indicates that sex allocation strategies are based on the ability to assess colony size quite accurately, an ability that occurs in several other allodapine genera, and which is likely to be ancestral for the tribe. The present study strengthens recent suggestions that complex sociality and sex allocation patterns are plesiomorphic traits for the allodapines, despite the ubiquity of small colony sizes.

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Group Size and Direct Fitness in Social Queues

Cited by 73 publications

References 45 publications

Helpers at the Nest Improve Late-Life Offspring Performance: Evidence from a Long-Term Study and a Cross-Foster Experiment

Helpers at the Nest Improve Late-Life Offspring Performance: Evidence from a Long-Term Study and a Cross-Foster Experiment

Reproductive Skew and the Origin of Sterile Castes

Cooperative nesting and complex female-biased sex allocation in a tropical allodapine bee

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