Skewed sex ratios and multiple founding in galls of the oak apple gall waspBiorhiza pallida

Abstract

Abstract. 1. The gall wasp Biorhiza pallida (Hymenoptera: Cynipidae) reproduces by cyclical parthenogenesis. The adults of the sexual generation develop within galls (oak apples) that contain many larval cells.2. Folliot [(1964) Annales Des Sciences Naturelles: Zoologie, 12, 407±564] found asexual generation females to be of three reproductive types. Androphores produce only sons, gynophores produce only daughters, and gynandrophores produce both sons and daughters. In nature, most oak apples give rise to either only males or only females but a proportion produces both sexes. These mixed-sex galls could result either from eggs laid by one or more gynandrophores or from eggs laid by androphores and gynophores developing within a single gall (multiple founding).3. Here the frequency of mixed-and single-sex galls was quantified, and morphological and genetic analyses were carried out on the adults emerging from 10 galls to determine the frequency of multiple founding in B. pallida.4. Seventy-five per cent of 627 galls yielded only one sex. The majority of the remaining 25% had a highly skewed sex ratio. Low genetic variation in B. pallida limited the application of allozyme-based genetic techniques, however seven of the 10 galls analysed in detail, including mixed-sex galls, appeared to have been multiply founded. Contributions by the different foundresses in multiply founded galls were highly skewed.5. The significance of multiple founding is discussed in the light of possible adaptive scenarios (reduction of parasitoid-induced mortality, avoidance of local stochastic extinction and inbreeding) and possible competition for oviposition sites.

Evidence for widespread cryptic sexual generations in apparently purely asexual Andricus gallwasps

“…Similar signatures could potentially be generated by other processes. Both misscoring of alleles and de novo mutation could result in recording different MLGs for sisters generated apomictically (Atkinson et al . 2003), which should have identical genotypes.…”

“…Oak and sycamore gallwasps are unique among CP arthropods in that their sexual and apomictic asexual generations are produced in strict alternation (Stone et al . 2002; Atkinson et al . 2003).…”

“…Most are known only from females whose morphology matches them to the apomictic generations of known CP species (Melika et al . 2000; Nieves‐Aldrey 2001; Atkinson et al . 2003), including all members of the genera Aphelonyx ( five species), Atrusca ( > 40 species) , Holocynips ( four species) , Odontocynips ( one species), Philonix ( seven species) , Phylloteras ( seven species) , Pseudoneuroterus ( one species) and Zopheroteras (six species) (Melika & Abrahamson 2000).…”

“…Asexual reproduction in oak cynipids results in siblings having identical MLGs to each other and to their mother (Atkinson et al . 2002, 2003). In species lacking a sexual generation, a single asexual generation gall will thus only yield more than one MLG when it contains the offspring of more than one female (i.e.…”

Longitudinal range expansion and cryptic eastern species in the western Palaearctic oak gallwasp, Andricus coriarius

“…2002). Most oak gallwasps have a cyclically parthenogenetic lifecycle (Atkinson et al . 2002, 2003) with a sexual generation in the spring and a parthenogenetic generation in the summer/autumn (Stone et al .…”