Territory quality drives intraspecific patterns of extrapair paternity

Despite the potential reproductive benefits of extrapair matings,extrapair paternity rates in many avian species often vary greatlyamong populations. Although ecological factors have been shownto influence intraspecific patterns of extrapair paternity insome species, for cooperatively breeding species living in familygroups, social/demographic factors may also play a role. Thisstudy examined how ecological factors related to territory quality(vegetation cover, insect abundance) and social/demographicfactors (group size, number of breeding pairs, genetic relatedness)influenced intraspecific patterns of extrapair paternity incooperatively breeding superb starlings, Lamprotornis superbus.Superb starlings inhabit spatiotemporally variable African savannaswhere high temporal variability drives reproductive decisions(adoption of breeding roles, offspring sex allocation) and whereterritories suitable for breeding are limited. Although extrapairpaternity rates were only 14% of offspring and 25% of nests,they varied greatly among groups, ranging from 4% to 32% ofoffspring and from 7% to 60% of nests. These among-group differencesin extrapair paternity were not related to social/demographicfactors but instead to territory quality; extrapair paternitywas higher on lower quality territories (lower vegetation coverand grasshopper abundance) than on higher quality territories(higher vegetation cover and grasshopper abundance). These resultssuggest that even in a heterogeneous landscape where suitablebreeding territories are limited, subtle differences in habitatquality can have profound effects on reproductive decisionsand patterns of extrapair paternity. Understanding the interactionbetween spatial (habitat heterogeneity) and temporal (temporalvariability) environmental variation will be important for determininghow environmental and social factors drive avian reproductiveand mating decisions.     

High fidelity on islands: a comparative study of extrapair paternity in passerine birds

It is commonly assumed that the intensity of sexual selectionis lower in island populations. Extrapair paternity (EPP) iswidespread within passerine birds and is indicative of sexualselection. A conservative analysis of the levels of EPP inisland and equivalent mainland populations of passerines revealsthat insular populations are indeed characterized by low levelsof EPP. This supports the idea that the intensity of sexualselection is lower on islands. This relationship has previouslybeen predicted, based on the assumption of low levels of geneticvariation for fitness in such populations. The evidence fromthis analysis suggests that this is just one of several nonmutuallyexclusive hypotheses that may explain the high fidelity of island-living females.     

Extrapair paternity and mate choice in a chickadee hybrid zone

The dynamics of hybrid zones are likely to be influenced greatlyby patterns of mate choice, including "cryptic" choice mediatedthrough extrapair copulations. To understand changes in hybridzones over time and space, a detailed examination of matingpatterns and correlates is needed. We studied the role of extrapairfertilizations (EPFs) in the breeding biology of hybridizingblack-capped and Carolina chickadees in southeastern Pennsylvaniaover 4 years, using microsatellite DNA markers. We detectedextrapair offspring (EPO) in 56% of 90 broods examined; theseaccounted for at least 26% of 477 offspring. Chickadees do notappear to use EPFs to reduce costs of heterospecific pairing:EPFs were no more likely to occur in genetically dissimilar(heterospecific) social pairs than in pairs where social mateswere genetically similar. However, females paired with black-capped–likemales were more likely to have EPO. Females that acquired EPFsdid not obtain these from males genetically similar to themselves;instead, all females, regardless of their genotype or that oftheir social mate, tended to prefer Carolina-like males as extrapairpartners. There was no relationship between the presence ofEPO and hatching or fledging success. High rates of extrapairpaternity and apparent female preference for Carolina-like malessuggest that mate choice is an important influence in ongoingnorthward movement of this hybrid zone.