Offspring sex ratio in the sequentially polygamous Penduline Tit Remiz pendulinus

Abstract

Despite the growing literature on facultative sex-ratio adjustment in chromosomal sex-determining vertebrate taxa (birds, mammals), the consistency of results is often low between studies and species. Here, we investigate the primary and secondary offspring sex ratio of a small passerine bird, the Eurasian Penduline Tit (Remiz pendulinus) in three consecutive years. This species has a uniquely diverse breeding system, in which the male (and/or the female) abandons the nest during egg-laying, and starts a new breeding attempt. This allowed us to test (1) whether patterns of parental care, i.e., male-only care, female-only care or biparental desertion, influence offspring sex ratio, and (2) whether the offspring sex ratio is repeatable between successive clutches of males and females. Using molecular markers to sex 497 offspring in 176 broods, we show that (1) offspring sex ratio does not depend on which parent provides care, and (2) the offspring sex ratio is not repeatable between clutches of a given individual. The overall primary and secondary offspring sex ratio at a population level is not different from parity (54 ± 6% males, and 50 ± 3% (mean ± SE), respectively). We suggest that ecological and phenotypic factors, rather than individual traits of parents, may influence offspring's sex, and conclude that there is currently no evidence for a facultative adjustment of offspring sex ratio in the Penduline Tit.

Levels of extra‐pair paternity are associated with parental care in penduline tits (Remizidae)

“…In line with our prediction, we found no evidence of a bias in the sex ratios of nestlings in the two biparental species (White-crowned Penduline Tit and Cape Penduline Tit). Although we cannot rule out the possibility of skewed sex ratios amongst adults, the low rates of EPP combined with biparental care found in these two species would be consistent with unbiased adult sex ratios (but see van Dijk et al 2008b showing parity of offspring sex ratio also in the polygamous Eurasian Penduline Tit). In most bird species, and especially small passerine birds, it is difficult to estimate adult sex ratios (Donald 2007).…”

No Evidence for Offspring Sex Ratio Adjustment in Marsh TitsPoecile palustrisBreeding in a Primeval Forest

“…Our study thus adds to a growing number of avian studies reporting no bias in brood sex ratios (Dietrich-Bischoff et al 2006, van Dijk et al 2008, Dyrcz & Cichoń 2009, Kingma et al 2011, review in Hasselquist & Kempenaers 2002, and Budden & Beissinger 2004. As such data are probably underrepresented in the published literature (Palmer 2000, Hasselquist & Kempenaers 2002 Table 1.…”

Nest desertion is not predicted by cuckoldry in the Eurasian penduline tit

“…Year, parental care strategy (male care, female care, and biparental desertion), sex of the offspring, and level of EPP (‘paternity’) were included in these models as fixed effects, and brood ID was included as a random effect. The sex of the offspring was, however, only known for the years 2002–2004 (van Dijk et al 2008). To improve sample sizes, we therefore also present the same LMM, excluding the sex of the offspring.…”