Nest defense in the face of cuckoldry: evolutionary rather than facultative adaptation to chronic paternity loss

Single fathers sacrifice their broods and re-mate quickly in a socially monogamous cichlid

When one of two parents disappears in the midst of caring for offspring, the remaining parent is left with several options. They can either (1) desert the brood, (2) continue caring on their own and reject propositions from new potential partners, or (3) continue caring but remain receptive to re-mating opportunities. The presence of a brood may increase re-mating success of single parents, either because brood care is perceived as a signal of partner quality, or because prospective mates perceive the brood as potential energy source. In this field experiment, we used the socially monogamous, biparental cichlid fish Variabilichromis moorii to examine the re-mating strategy of males with or without dependent offspring after the loss of their female partner. Partner vacancies were filled quickly by new females, and these females engaged in high levels of affiliative behavior with the males. The new females engaged in territorial defense, but focused primarily against intruding conspecifics, likely as a means to repel rivals. The males, in turn, took over the majority of territorial defense against intruding heterospecifics. Interestingly, males that still had offspring from their previous partnerships did not show aggression toward their new female partners, even when those females were infanticidal and cannibalizing the males' current offspring. Overall, our experiment shows that single fathers of a biparental species will re-mate quickly even at the detriment to their current offspring.

Seasonal variation in cuckoldry rates in the socially monogamous cichlid fish Variabilichromis moorii

Mating patterns in animal populations can respond to environmental conditions and consequently vary across time. To examine this variation in nature, studies must include temporal replicates from the same population. Here, we report temporal variation in genetic parentage in the socially monogamous cichlid Variabilichromis moorii from Lake Tanganyika, using samples of broods and their brood-tending parents that were collected across five field trips from the same study population. The sampled broods were either spawned during the dry season (three field trips) or during the rainy season (two trips). In all seasons, we detected substantial rates of extra-pair paternity, which were ascribed to cuckoldry by bachelor males. Paternity shares of brood-tending males were consistently higher, and the numbers of sires per brood were consistently lower, in broods that were spawned in the dry seasons compared to broods from the rainy seasons. In contrast, the strength of size-assortative pairing in our V. moorii population did not vary temporally. Seasonal fluctuations in environmental conditions, such as water turbidity, are proposed as a mechanism behind variable cuckolder pressure. Our data demonstrate the utility of long-term monitoring to improve our understanding of animal mating patterns.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10750-022-05042-0.

Freshwater hydrozoan blooms alter activity and behaviour of territorial cichlids in Lake Tanganyika

Blooms of gelatinous zooplankton can represent dramatic environmental perturbations for aquatic ecosystems. Yet, we still know little about how blooms impact fitness-related behaviours of fish caught within their areas of effect, especially for freshwater systems. Here, we documented the behavioural impacts of freshwater hydrozoan (Limnocnida tanganjicae) blooms on a territorial cichlid (Variabilichromis moorii), as well as on the wider community of cichlids in a shallow-water rocky habitat of Lake Tanganyika. Compared with non-bloom conditions, V. moorii individuals in the midst of blooms reduced their swimming and territory defence activities (each by approx. 50%) but not their foraging or affiliative behaviours. Despite this reduction in activity, V. moorii could not entirely avoid being stung and preferred to remain closer to the rocky substrata as opposed to the more open demersal zone. Many other fishes similarly hid among the benthic substrata, changing the composition of the fish community in the demersal zone during bloom conditions. Reductions in activity could have multiple fitness-related implications for individual fish. Establishing the consequences of these behavioural changes is important for understanding the effects of gelatinous zooplankton blooms in freshwater systems.