Two strains of male-killing Wolbachia in a ladybird, Coccinella undecimpunctata, from a hot climate

Abstract

Ladybirds are a hot-spot for the invasion of male-killing bacteria. These maternally inherited endosymbionts cause the death of male host embryos, to the benefit of female sibling hosts and the bacteria that they contain. Previous studies have shown that high temperatures can eradicate male-killers from ladybirds, leaving the host free from infection. Here we report the discovery of two maternally inherited sex ratio distorters in populations of a coccinellid, Coccinella undecimpunctata, from a hot lowland region of the Middle East. DNA sequence analysis indicates that the male killing is the result of infection by Wolbachia, that the trait is tetracycline sensitive, and that two distinct strains of Wolbachia co-occur within one beetle population. We discuss the implications of these findings for theories of male-killing and suggest avenues for future field-work on this system.

Figure 1. Egg hatch rates and progeny sex ratios (± standard errors) of matrilines of C. undecimpunctata.

Hatch rate was measured by comparing the number of hatched eggs (H) to the total number of laid eggs (hatched+grey+yellow). The matrilines are labelled as follows: Egypt 2004 - A-G with diamond symbol; Egypt 2005 - E1–E4 with triangle symbol; and Jordan - J1–J5 with square symbol.

Figure 2. C. undecimpunctata matrilines females & F1 females sex ratio (proportion of male offspring) with standard error.

Matrilines are labeled as in Figure 1. The letter “S” and the circle symbol represent all lines that have zero sex ratio in both F1 and F2 from the three collections (B, E1, E2, E3, J2 & J4).

Figure 3. Phylogenetic tree of wsp DNA sequence data of Wolbachia hosted by different species.

Maximum parsimony-based bootstrap analysis of different hosts of Wolbachia including the two Wolbachia strains of the C. undecimpunctata. Bootstrap values are indicated above the branches. Wolbachia strains are represented by the names of their host species, their phenotype where known (CI = cytoplasmic incompatibility; PI = parthenogenesis inducing; F = feminizing; MK = male-killing) and Genebank accession numbers. Suffix letters for A. bipunctata refer to the two different Wolbachia sequences, lodged by Hurst et al. (1999b). The wsp sequences found in this study are the Coccinella 11-punctata E (MK) EF502046 and Coccinella 11-punctata J (MK) EF608161 (in bold). Wolbachia wsp sequences used in constructing this tree were obtained from the Entrez Nucleotide database.