Mating system and extra-pair paternity in the Fan-tailed Gerygone Gerygone flavolateralis in relation to parasitism by the Shining Bronze-cuckoo Chalcites lucidus

Abstract

Extra-pair copulation can increase genetic diversity and offspring fitness. However, it may also increase intra-nest variability in avian hosts of brood parasites, which can decrease the discrimination ability of host parents towards the parasite. In New Caledonia, the Fan-tailed Gerygone (Gerygone flavolateralis), which is parasitized by the Shining Bronze-cuckoo (Chalcites lucidus), has two nestling morphs, dark and bright, that can occur in monomorphic and polymorphic broods. Gerygone parents recognize and eject parasite nestlings from their nest, but the presence of polymorphic broods may increase the chances of recognition errors. Using 17 microsatellite markers, we investigated the mating system of the Fan-tailed Gerygone to understand the mechanisms underlying nestling polymorphism. We hypothesised that extra-pair copulations would lead to a higher proportion of polymorphic broods caused by higher genetic variability, thus creating a trade-off between genetic benefits and host defence reliability. Extra-pair paternity occurred in 6 of 36 broods, which resulted in 6 of 69 offspring sired by extra-pair males. Broods with and without mixed paternity were comparably often parasitized. Extra-pair paternity did not influence the proportions of bright, dark and polymorphic broods. Compared to bright siblings in polymorphic broods, dark nestlings tended to have lower heterozygosity, particularly in loci associated with skin coloration. The results also suggested that there is no obstacle for genetic exchange between individuals from forest and savannah, possibly due to dispersal of offspring. We conclude that the Fan-tailed Gerygone is a socially monogamous species with a low rate of extra-pair paternity compared to closely related species. Extra-pair paternity increased offspring genetic variability without measurable associated costs by brood parasitism. The results highlight the importance of studying host mating systems to assess the trade-offs between host defence and offspring fitness in co-evolutionary arms races.

Visual discrimination of polymorphic nestlings in a cuckoo-host system

“…Thus, nestling phenotypes may change if parents exchange partners or incur in extra-pair copulations and this may strongly constrain the selective advantage of nestling polymorphism as a host defence. In the Fan-tailed Gerygone, extra-pair copulations had however no impact on the frequency of nestling or brood types 39 . Nevertheless, polymorphic broods may have further promoted the arms race, which involves generalist mimicry by the parasite and true-recognition based on multiple sensorial cues by the host.…”

“…In contrast to Australian Gerygone species, Fan-tailed Gerygone have two distinct nestling morphs, with a pinkish-grey (bright) or a darkish-brown (dark) skin, which can occur in monomorphic and polymorphic broods 37 , 39 . Brood colouration can vary within broods of the same parents, however it is most often constant for the same pair across multiple breeding attempts and extra-pair copulations do not influence the proportions of bright, dark or polymorphic broods 39 . The Shining Bronze-cuckoo from New Caledonia also has two nestling morphs, dark and bright 37 .…”

Impact of brood parasitism and predation on nest survival of the fan‐tailed gerygone in New Caledonia

“…Pairs of the fan‐tailed gerygone are socially monogamous and use the same territory over several breeding seasons (Bojarska et al , Attisano et al ). The average clutch size is 2.1 ± 0.1 (all averages with 95% confidence intervals) eggs, the incubation phase is 18 ± 1 days and the nestling phase is 14 ± 1 days (Attisano et al ).…”

Almost faithful: SNP markers reveal low levels of extra-pair paternity in the Eurasian beavers

“…Studies using molecular techniques have revealed that social monogamy does indeed not necessarily imply genetic monogamy: while 90% of bird species are socially monogamous (Cockburn 2006), out of these, less than 25% are also genetically monogamous (reviewed in Griffith et al 2002, Bojarska et al 2018. In comparison, monogamy in mammals is less common and only 3-9% of the species are defined as socially monogamous (Trivers 1972, Lukas and.…”