Biased sex ratio and niche restriction in Baruscapillaria obsignata (Madsen 1945) (Nematoda, Capillariidae) from Columba livia (Aves, Columbidae)

Abstract

In the present study populations of the avian nematode species Baruscapillaria obsignata are described from Columba livia. Male and female individuals were obtained from 27 birds, fixed in alcohol/formalin/acetic acid (AFA) and preserved in 70% ethanol. Nematodes were identified and then counted under a stereoscopic microscope. Baruscapillaria obsignata were much more frequent in the anterior third of the small intestine, and females were more abundant than males in all infra populations. The prevalence was 55.6%, mean intensity was 11.8 (median 11.0; range 1-31) and abundance 6.56. In the present study, we observed an aggregated distribution of parasite infrapopulations, as demonstrated by the value of the exponent of the negative binomial distribution, K = 0.2773; by the discrepancy index, D = 0.656 and by the variance/mean ratio, 12.44. The female/male sex ratios found in all infrapopulations were always greater than 1, showing a bias in favour of female abundance. This tendency was especially marked in infrapopulations containing fewer individuals. The sizes of infrapopulations ranged from 5 to 31 individuals. The mean sex ratio observed was 2.69 ± 3.28 (median 1.83; range 0-11). In infrapopulations with 5-15 individuals, the sex ratios observed varied from 2.6 to 11, while in those with 17-31 individuals, the sex ratios were lower, ranging from 1.7 to 2.4. There was a negative correlation between the intensity of infection and the sex ratio of infrapopulations. Results are discussed in terms of possible factors influencing the processes that lead to niche restriction and biased sex ratios in parasite infrapopulations.

Brazilian Angiostrongylus cantonensis haplotypes, ac8 and ac9, have two different biological and morphological profiles

“…In dioecious helminths, males and females do not always fit a 1:1 ratio. The number of female specimens may be favoured in small populations, but this trend can change if the intensity of infection increases, as observed in previous studies ( Poulin 1997 , D‘Ávila et al 2012 , Rishniw et al 2012 ). Poulin (1997) analysed the relationship between sex ratio and intensity of infection in nematode species, observing a female bias in natural populations.…”

Plant‐parasitic nematodes as invasive species: characteristics, uncertainty and biosecurity implications

“…This mechanism may affect the establishment and persistence of invasive PPN by altering resource use efficiency, but further studies are required to determine if there is a correlation with invasion success. Observations in animal‐parasitic nematodes of variation in sex ratios relative to level of infection, host size and temperature have also been linked to reduced competition for food and hence success in invasion of the host (D'Ávila et al , ; Golestaninasab et al , ).…”

Extrinsic- and intrinsic-dependent variation in component communities and patterns of aggregations in helminth parasites of great cormorant (Phalacrocorax carbo) from N.E. Poland

“…are necessary to understand these processes. In recent literature, such analyses concerning helminth parasites are extremely rare (Newey et al 2005; Marques et al 2010); in avian hosts, the issue has been investigated only to a limited extent (Kanarek 2011; D’Ávila et al 2012). …”