Ecology,Wolbachiainfection frequency and mode of reproduction in the parasitoid waspTetrastichus coeruleus(Hymenoptera: Eulophidae)

Abstract

Whereas sexual reproduction may facilitate adaptation to complex environments with many biotic interactions, simplified environments are expected to favour asexual reproduction. In agreement with this, recent studies on invertebrates have shown a prevalence of asexual species in agricultural (simplified) but not in natural (complex) environments. We investigated whether the same correlation between reproductive mode and habitat can be found in different populations within one species. The parasitoid wasp Tetrastichus coeruleus forms an ideal model to test this question, since it occurs both in natural and agricultural environments. Further, we investigated whether Wolbachia infection caused parthenogenesis in female-biased populations. In contrast to the general pattern, in Dutch and French natural areas, we found Wolbachia-infected, highly female-biased populations that reproduce parthenogenetically. In contrast, populations on Dutch agricultural fields were not infected with Wolbachia, showed higher frequencies of males and reproduced sexually. However, we also found a female-only, Wolbachia-infected population on agricultural fields in north-eastern United States. All Wolbachia-infected populations were infected with the same Wolbachia strain. At this moment, we do not have a convincing explanation for this deviation from the general pattern of ecology and reproductive mode. It may be that asparagus agricultural fields differ from other crop fields in ways that favour sexual reproduction. Alternatively, Wolbachia may manipulate life history traits in its host, resulting in different fitness pay-offs in different habitats. The fixation of Wolbachia in the United States populations (where the species was introduced) may be due to founder effect and lack of uninfected, sexual source populations.

Tracing the history and ecological context of Wolbachia double infection in a specialist host (Urophora cardui)—parasitoid (Eurytoma serratulae) system

“…For the U. cardui strain Ucar_A1, the most related strain infests the weevil Ceutorhynchus obstrictus (2bp difference), which is associated with Brassica (cabbage). For U. stylata , the identical MLST stain (save for 1bp) has been found in three Lepidoptera, the European paper wasp, and the asparagus beetle parasitoid Tetrastichus coeruleus (MLST databank; Reumer, Van Alphen, & Kraaijeveld, 2010). This multihost pattern is typical for Wolbachia .…”

Parthenogenesis and developmental constraints

“…In contrast, in solitary hymenopterans and also in some mites and thysanurans, the switch to thelytoky is usually induced by maternally transmitted endosymbionts (usually Wolbachia), that in this way increase their transmission rate (Stouthamer, Luck, & Hamilton, 1990;Werren et al, 2008). Although it is thought that selection for resistance in hosts often leads to the loss of Wolbachia (Reumer, Van Alphen, & Kraaijeveld, 2010;Werren & Windsor, 2000;Werren et al, 2008), this does not necessarily lead to the loss of thelytoky, due to the reduced sexual functioning, which keeps the females locked into thelytoky (Stouthamer et al, 2010;Werren, 1997;Werren et al, 2008). Over time the sexual reproductivity of infected females generally declines due to the accumulation of deleterious mutations, thus creating a reproductive barrier between infected and uninfected populations (Pannebakker et al, 2005;Stouthamer, Russell, Vavre, & Nunney, 2010;Werren, 1998).…”

Reduced sexual functionality of PI‐Wolbachia‐infected females of Tetrastichus coeruleus

“…The parasitoid wasp Tetrastichus coeruleus (Nees) (Hymenoptera: Eulophidae) forms an ideal model to study the decay of sexual functionality, because it has both arrhenotokous and thelytokous populations (Reumer et al, 2010). Tetrastichus coeruleus is an egg-larval parasitoid of the common asparagus beetle, Crioceris asparagi (L.).…”

“…Tetrastichus coeruleus is an egg-larval parasitoid of the common asparagus beetle, Crioceris asparagi (L.). We sampled T. coeruleus in The Netherlands, Belgium, southern France, and Massachusetts, USA (Reumer et al, 2010). Asparagus officinalis is native to western Asia, Europe, and northern Africa, and has been introduced to North-and South-America for culturing (Audas & Heywood, 1981;Weeda et al, 1991).…”

“…Crioceris asparagi lives on the asparagus plant (Asparagus officinalis L.), which grows on sandy soils, such as coastal dune areas, and as a crop in monoculture on agricultural fields. Populations from the Dutch coastal dune areas are infected with Wolbachia and reproduce parthenogenetically (thelytoky), whereas populations from the Dutch and Belgian agricultural fields are not infected and reproduce sexually (arrhenotoky) (Reumer et al, 2010). We sampled T. coeruleus in The Netherlands, Belgium, southern France, and Massachusetts, USA (Reumer et al, 2010).…”