How host size may constrain the evolution of parasite body size and clutch size. The parasitic isopod Ichthyoxenus fushanensis and its host fish, Varicorhinus bacbatulus, as an example

Abstract

The flesh‐burrowing parasitic isopod Ichthyoxenus fushanensis was found infecting the body cavity of a freshwater fish, Varicorhinus bacbatulus, in heterosexual pairs. Herein we investigate the question of how the host body size may constrain the parasite size and clutch size by analyzing the interactions among the body size and clutch size of the parasite, and host size. Due to the low transmission rate of I. fushanensis to its host and the positive relationship between clutch size and female size, selection may favor larger females with larger clutch sizes to compensate for massive losses of manca (the free‐living juveniles). The path model reveals that clutch size depends not only directly on female size, but also on the sizes of her host and mate. Female size also depends on the sizes of the host and her mate. A negative correlation exists between the body sizes of the paired males and females. This negative correlation may be regarded as a consequence of competition for limited available space or other resources provided by the host. The effects of host size on parasite size, however, act on the total volume of both sexes as a whole, not specifically on either the female or the male. In this case, the available space/resources may not allow both individuals of different sexes to evolve toward a larger size simultaneously. Under the constraint of host size, a strategy of reducing the body size of the paired male may provide a way to increase the body size of the paired female and achieve a larger clutch size.

Which factors regulate the reproduction of ectoparasites of temperate-zone cave-dwelling bats?

“…Reproduction is the most energetically demanding phase of a parasitic life cycle (Combes 2001;Tinsley 2004), and since parasites entirely depend on the amount and quality of nutrients provided by their hosts, it is expectable that host-dependent factors play an important role in regulating the parasitic reproductive processes. Indeed, the reproductive activity of parasites has been shown to be greatly affected by the general quality of their hosts, on the basis of host age, size, diet, immune status, or condition (e.g., Ito et al 1986;Crompton 1987;Quinnell 1988;Poulin 1996;Tsai et al 2001;Seppälä et al 2008). On the other hand, because hosts are often scarce or widely distributed, parasites had to evolve a number of strategies to reproduce successfully, for instance, a high reproductive rate that compensates for their enormous losses while locating and establishing within a host (Kennedy 1975;Combes 2001;Tinsley 2004).…”

Influence of ecological role on bathymetric patterns of deep-sea species: size clines in parasitic gastropods

“…This unimodal pattern is very similar to that reported for gastropods along the same transect . Tsai et al (2001) demonstrated that host body size dictates the total parasite biomass possessed by the host. Yet a given biomass can produce a number of density and size distribution relationships (Allen et al 2002).…”

“…Thus, increases in host body size, i.e. greater resource availability, can lead to either a greater parasite load (Poulin & Rohde 1997, Poulin 1999, Poulin & Valtonen 2001, George-Nascimento et al 2004 or larger parasite body sizes (Morand et al 1996, Poulin 1996, Tsai et al 2001, or various combinations of the 2 alternatives. Interestingly, the euliimids display no pattern in size despite the increased size over depth in echinoderms, suggesting increased resource availability manifests itself in greater parasite density.…”

Population differences in host use by a seed-beetle: local adaptation, phenotypic plasticity and maternal effects

“…For insects that use discrete resources, such as parasitoids and seed feeders, host size and host quality are major sources of phenotypic variation among host species and may constrain offspring growth, influencing the evolution of body size and life history traits (Hardy et al 1992;Allen and Hunt 2001;Mackauer and Chau 2001;Tsai et al 2001). In species with scramble competition, individuals in populations adapted to large hosts are generally larger than those adapted to small hosts, generating genetic variation in body size among populations adapted to different hosts (Toquenaga and Fuji 1990).…”