Intraspecific density-dependent effects on growth and fecundity of Diplosentis nudus (Harada, 1938) Pichelin et Cribb, 2001 (Acanthocephala, Cavisomidae)

Abstract

During June and July of 2007, a total of 130 specimens of the fish Rastrelliger kanagurta Cuvier (Teleostei, Scombridae), ranging between 19-31 cm in total length, were caught in the Red Sea off the coast of Sharm El-Sheikh, South Sinai, Egypt, and examined for infections by acanthocephalans (65 fish/month). Of this number, 29 (22.30%) were slightly or heavily parasitized by the acanthocephalan Diplosentis nudus (Harada, 1938) Pichelin et Cribb, 2001; no other helminth parasites were found in the intestine of R. kanagurta. Twenty-nine infrapopulations of D. nudus, ranging from 23-218 individuals were collected from the infected fishes. These infrapopulations were distributed in a well-defined fundamental niche along the intestine of R. kanagurta, where the distribution of male worms was not random with respect to female worms size and position and suggests that the male-male competition for access to female may be intense and may select for large males. No correlation between fish size and infrapopulation size was observed. Correlations between female-to-male sex ratio and infrapopulation size, numbers of females and their mean lengths, numbers of males and their mean lengths, mean female length and mean male length within infrapopulation were very strong, and clearly suggest that as the infrapopulation size increased, the number of females and their mean lengths decreased and the number of males and their mean lengths increased. Combination of these results strongly suggests density-dependent effects and competition between male worms. The relationship between the mean female length or size and the number of eggs within its pseudocoel was strongly positive; egg production by female worm significantly decreases as the infrapopulation size increases, suggesting density-dependent reduction in female worm fecundity. Tendency for the variability in male testes size was not significant in infrapopulations of D. nudus. All of these results are discussed.

Is a vertebrate a better host for a parasite than an invertebrate host? Fecundity of Proctoeces cf lintoni (Digenea: Fellodistomidae), a parasite of fish and gastropods in northern Chile

“…Our results are consistent with the expected relationships between worm size and fecundity, i.e., larger parasites harbored higher numbers of eggs (El-S.Hassanine and Al-Jahdali 2008;Rowe et al 2008;Hanelt 2009 among many others) but only for the invertebrate host. However, worm size and fecundity were higher (but not significantly) for S. sanguineus, and the suggested negative relationship between parasite density (abundance) and fecundity (Shostak and Scott 1993;El-S. Hassanine and Al-Jahdali 2008) was not evident in our data set, suggesting that fecundity was independent of parasite abundance for all studied hosts.…”

Interference competition in entomopathogenic nematodes: male Steinernema kill members of their own and other species

“…Best documented are the interspecific interactions, including predation, between larval trematodes in snails (Lie et al, 1968;Lim and Heyneman, 1972;Hechinger et al, 2011). Homosexual rape has been documented in acanthocephalans, where cementing of the male victim's genital region effectively removed it from the reproductive population (Abele and Gilchrist, 1977;Hassanine and Al-Jahdali, 2008). While this is viewed by some as merely evidence of indiscriminate mating (Richardson et al, 1997), the fact that there is intense malemale competition for mates in the Acanthocephala (Poulin and Morand, 2000;Sinisalo et al, 2004) lends weight to the suggestion (Abele and Gilchrist, 1977) that it is sexually selected behaviour.…”

Infrapopulations ofSclerocollum saudiiAl-Jahdali, 2010 (Acanthocephala: Cavisomidae) in the rabbitfishSiganus rivulatus(Teleostei, Siganidae) from the Saudi coast of the Red Sea

“…Density-dependent reductions in mean worm length (growth or fecundity) have been reported in several studies (e.g. Szalai & Dick, 1989;Shostak & Scott, 1993;Richards & Lewis, 2001;Dezfuli et al, 2002;Poulin et al, 2003;Hassanine & Al-Jahdali, 2008). Such a decrease in length (fecundity) contributes to the regulation of the parasite population by the availability of infective stages for all infrapopulations (Poulin, 2006).…”

“…Undoubtedly, the fundamental niche of a gastrointestinal helminth parasite has a carrying capacity, i.e. has a capacity for a certain maximum number of worms that can exist within it without intraspecific competition (Hassanine & Al-Jahdali, 2008). In small infrapopulations of S. saudii the female-male ratios were female-biased; where the intensity was slight or moderate, the immature and mature worms were in separate sites within the fundamental niche and the density-dependent effects were not noticeable.…”