Individuals within groups of cooperatively breeding species may partition reproduction, with the dominant pair often taking the largest share. The dominant's ability to reproductively control subordinates may depend on differences in competitive ability, due to, e.g. body size differences, but may also depend on the number of same-sex competitors inside the group. We tested experimentally whether subordinates reproduce more when these subordinates are large or when a second subordinate of the same sex need to be controlled by the dominants, using the cooperatively breeding cichlid Neolamprologus pulcher. Dominant pairs were assisted by a large and a small unrelated subordinate; sexes of these fish were varied in a full-factorial design (giving four treatments). Dominant males lost significantly more parentage to the large subordinate male when a small subordinate male was also present, compared to when a small subordinate female was present. However, subordinate paternity was generally low and did not significantly curb total dominant male reproductive output, which was more affected by the sizes and numbers of reproductive females present inside his group. Dominant female maternity, clutch sizes and total output did not depend on the treatments. Subordinate-subordinate reproduction was virtually absent (one out of 874 offspring). Female subordinates were more likely to provide care for their own broods. In contrast, male subordinates did not adjust their level of care to their parentage. Variability in female subordinate alloparental brood care was particularly high, with females showing more care than males in general. We also detected effects of growth rate and food ration on parentage independent of the treatments, most notably: (i) a trade-off between dominant male growth rate and paternity; (ii) a decrease in dominant male paternity with increasing food ration; (iii) a positive effect of growth rate on paternity in small males. We conclude that dominant males should be sensitive to the number and sizes of subordinate males present in their group, particularly when these subordinates are not helpful or grow fast, and food is plentiful. Dominant females should be less sensitive, because female subordinates do not appear to impose reproductive costs and can be helpful through alloparental brood care.

BackgroundIn many cooperatively breeding vertebrates, subordinates assist a dominant pair to raise the dominants' offspring. Previously, it has been suggested that subordinates may help in payment for continued residency on the territory (the ‘pay-to-stay hypothesis’), but payment might also be reciprocated or might allow subordinates access to reproductive opportunities.Methodology/Principal FindingsWe measured dominant and subordinate female alloparental brood care and reproductive success in four separate experiments and show that unrelated female dominant and subordinate cichlid fish care for each other's broods (alloparental brood care), but that there is no evidence for reciprocal ‘altruism’ (no correlation between alloparental care received and given). Instead, subordinate females appear to pay with alloparental care for own direct reproduction.Conclusions/SignificanceOur results suggest subordinate females pay with alloparental care to ensure access to the breeding substrate and thereby increase their opportunities to lay their own clutches. Subordinates' eggs are laid, on average, five days after the dominant female has produced her first brood. We suggest that immediate reproductive benefits need to be considered in tests of the pay-to-stay hypothesis.

When social groups monopolize discrete habitat patches, group size may be positively correlated with patch size. The correlation can be a direct consequence of limited resources. Alternatively, it can be an indirect consequence of patch-size effects on a dominant group member. We asked which of these two mechanisms was responsible for a positive correlation between the group size of false clown anemonefish (Amphiprion ocellaris Cuvier in Cuvier and Valenciennes, 1830) and that of the host sea anemone Stichodactyla gigantea (Forskål, 1775). We argue that some false clown anemonefish groups may have reached the carrying capacities of their hosts, but that the group size : patch size correlation in the population as a whole is best interpreted as an indirect consequence of a positive relationship between anemone size and the length of the dominant group member. The dominant's length in turn limits group size because dominant group members inhibit the growth of their subordinates. Thus, a correlation between group size and patch size need not imply resource limitation of subordinate group members.

In cooperatively-breeding species, the sexes of subordinate group members may have important consequences for dominant individuals. We varied subordinates' sexes in aquariumhoused groups of the cooperatively-breeding cichlid fish Neolamprologus pulcher, and compared the behaviours of dominant individuals in groups with same-versus oppositesex subordinates. Dominants tended to be more aggressive towards same-sex subordinates, and dominant males directed more affiliative behaviour towards large female subordinates. These patterns suggest that mixed-sex groups can be viewed as separate male and female dominance hierarchies. Aggressive and affiliative interactions between dominant males and dominant females were more frequent when a large subordinate was female, which indicates that subordinates can be a source of conflict between the members of a breeding pair. Finally, subordinates' sexes affected dominants' locations within aquaria and the performance of territory maintenance behaviour by dominant females. In many cases, the effect of one subordinate's sex depended on a second subordinate's sex or on group members' absolute or relative body sizes. Therefore, predicting effects of subordinates' sexes in larger, more variable groups will be challenging. Our results are the first to experimentally demonstrate the importance of a group's gender composition for the behaviour of dominant individuals in a cooperatively-breeding species.

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Abstract:The generalization that quagga mussel (Dreissena bugensis) and zebra mussel (Dreissena polymorpha) occur in deep-cold water and shallow-warm water, respectively, is inappropriate. We estimated dreissenid densities at sites affected by warmwater discharges into Lake Erie (Nanticoke, Ontario) to separate the effects of depth and temperature. Both species' densities increased with depth. After controlling for depth, quagga mussel were more abundant at thermally enriched sites than at sites unaffected by the discharge. This suggests that quagga mussel may occur in deep water not because such sites are cooler in summer, but because they are warmer over winter because of the inverse stratification in the range 0-4°C. Zebra mussels were unaffected by the warmwater plume at a broad scale, but were almost entirely absent from a site at the mouth of the discharge canal. This is inconsistent with previous indications that zebra mussel can tolerate higher temperatures than quagga mussel. Even in shallow water unaffected by the discharge, quagga mussel were more abundant than zebra mussel. Because Nanticoke was among the first places in North America to be colonized by quagga mussel, their numerical dominance at Nanticoke may be followed by similar changes in other nearshore areas of the lower Great Lakes.Résumé : La généralisation selon laquelle la moule quagga (Dreissena bugensis) et la moule zébrée (Dreissena polymorpha) se retrouvent dans des eaux froides et profondes et dans des eaux chaudes et peu profondes, respectivement, ne tient pas. Afin de distinguer les effets de la température de ceux de la profondeur, nous avons estimé la densité des dreissénidés dans des stations du lac Érié soumises à des rejets d'eaux chaudes, à Nanticoke (Ontario). Pour les deux espèces, la densité augmentait avec la profondeur. Une fois éliminé l'effet de la profondeur, la moule quagga était plus abondante dans les stations enrichies par la chaleur que dans celles non soumises au rejets. Il est donc possible que ce mollusque se retrouve dans les eaux profondes non pas parce que celles-ci sont plus froides en été, mais parce qu'elles sont plus chaudes en hiver à cause de la stratification inverse des eaux de 0 à 4ºC. Le panache d'eaux chaudes n'avait aucun effet à grande échelle sur la moule zébrée, mais cette espèce était presque complètement absente d'une station située à l'embouchure de l'émissaire. Ces constatations contredisent les indications antérieures selon lesquelles la moule zébrée pourrait tolérer des températures plus élevées que la moule quagga. Même dans les eaux peu profondes non touchées par les rejets, la moule quagga était plus abondante que la moule zébrée. Comme Nanticoke est une des premières localités nord-américaines à être envahie par la moule quagga, la dominance numérique de cette espèce à Nanticoke risque d'être suivie d'une évolution semblable dans d'autres zones côtières des Grands Lacs inférieurs. [Traduit par la Rédaction]

A complete method to regenerate adventitious shoots and to produce field-ready trees from three commercial cultivars of sweet cherry (Prunus avium L.) is described. The effects of explant types, pre-treatments, basal media, and phloroglucinol on cultivars Bing, Sweetheart, and Lapins were investigated. Callus developed on four explant types: apical shoot tips isolated from orchard trees; and punctured shoot tips, stem sections, and shoot bases of in vitro shoot cultures. Callus formed on Bing (5%), Sweetheart (8%), and Lapins (20%) shoot tips from orchard trees after 4 months on Murashige and Skoog medium (MS) at half-strength with 3 mM benzylaminopurine (BA). In vitro-derived explants formed callus after 3 months on Woody Plant Medium with 3 mM BA (W3B): punctured shoot tips (Sweetheart and Lapins 67%), stem sections (Sweetheart 31%, Lapins 27%), and shoot bases (Sweetheart 10%, Lapins 17%). Pre-treatment of shoot cultures on MS with 3 mM BA and 1 mM phloroglucinol increased callus formation three-fold on shoot base explants. Callus was separated from parental explants and maintained on MS with 3 mM BA. Shooting was induced by transferring callus to W3B. At 2 weeks, shoot development approached 100%. By 4 weeks, 7-17 shoots had formed on each explant. Callus was maintained for 1.5 years with no decrease in shoot production. Shoots were grafted onto Mazzard (P. avium) rootstocks with 54% (Sweetheart), 57% (Lapins), and 21% (Bing) success after 5 weeks.

In group‐living species, a dominant male’s ability to monopolize reproduction, and the cost of doing so, are expected to vary with a group’s gender composition. We used spawning observations of a group‐living cichlid, Neolamprologus pulcher, to test this expectation. We constructed groups that contained a dominant breeding pair and either two male subordinates, one male and one female subordinate or two female subordinates. Parasitic spawning by male subordinates was more common in groups with two male subordinates than in groups with one male and one female subordinate. Female subordinates were never observed laying eggs in dominant females’ clutches, but three female subordinates laid independent clutches. During spawning, frequencies of dominant male aggression towards male and female subordinates were similar. Dominant males were less aggressive during non‐reproductive periods. The declines were greater for female subordinates, such that, during non‐reproductive periods, dominant males were more aggressive towards male subordinates. Aggression towards each subordinate was also affected by the second subordinate’s gender; the direction of that effect differed for large and small subordinates. Male subordinates approached breeding shelters less often than female subordinates, and both male and female subordinates approached shelters more frequently when the second subordinate was male. Collectively, these patterns suggest: (1) that male subordinates impose higher costs on dominant males than female subordinates do and (2) that the presence of a second male subordinate imposes additional costs beyond those of the first male subordinate. We discuss the implications of these effects for dominant and subordinate group members.