Sex ratio and morphological polymorphism in an isolated, endemicTeladorsagia circumcinctapopulation

Abstract

Teladorsagia circumcincta is a polygamous nematode that exhibits morphological polymorphism. Sex ratio is typically female biased and the male nematodes occur in association with the genetically similar, minor morphotypes Teladorsagia davtiani and Teladorsagia trifurcata. In experimental infections, sex ratio (proportion male) and the proportion of minor male morphs observed have been shown to be influenced by both host and nematode-related factors. As similar investigations from natural systems are rare, this study examined whether sex ratio and minor male morph frequency were associated with host age and sex and nematode infra-population size in the isolated Soay sheep population on St Kilda. Count data for Teladorsagia were analysed for sheep of all age classes and both sexes from the winters of three consecutive population crashes (1999, 2002 and 2005). Generally, the intensity of Teladorsagia nematodes increased with host age until the age of 2 years before decreasing. In 2005, abundance of nematodes was generally higher than in the previous crashes, nematode sex ratio was negatively associated with host age and tended to be negatively associated with nematode intensity. Within the male nematode subpopulation, T. circumcincta always predominated, followed by T. davtiani and then T. trifurcata, with little variation in the relative proportions between hosts. The presence of each minor morph was primarily associated with the intensity of male T. circumcincta and, in those hosts where all three male morphs were detected, intensity of each minor morph was most associated with intensity of Teladorsagia females. Therefore, in a year when the nematode was generally more abundant, sex ratio appeared to be influenced by both host and nematode-related factors, whereas in all years examined, the frequency of morphological polymorphism was primarily density dependent.

Identification and characterization of alternative splicing in parasitic nematode transcriptomes

“…In the case of T. colubriformis , material was obtained from an inbred laboratory strain [25], while O. flexuosa and T. circumcinta material were collected in the field [28,29]. O. flexuosa nodules tend to be dominated by large, adult females [55]. Likewise, T. circumcinta is a polymorphic species with sex ratios biased towards females [56].…”

Evolution of alternative male morphotypes in oxyurid nematodes: a case of convergence?

“…Male dimorphism is also quite common in Ostertagiinae nematodes (Hoberg & Abrams, ; Grillo et al ., ; Hoberg et al ., ). In one representative of this group, Teladorsagia circumcincta , the frequency of morphological polymorphism is primarily density dependent, with minor male morphs more likely to occur in high intensity infections, their intensity being positively correlated with that of the larger morph (Craig et al ., ). However, differences in mating tactics of the different male morphotypes are still unknown among nematodes.…”

Lepus corsicanus gastro-intestinal helminths: first report

“…T.c. circumcincta and T. c. trifurcata have been definitely recognized as morphotypes of the same species (Leignel et al, 2002) that always occurs in host population in more or less fixed proportion with predominant T. c. circumcincta (Craig et al, 2010). They are typical parasites of ruminants and have never been found in naturally infected lagomorphs.…”