Female Gnathia marleyi (Isopoda: Gnathiidae) feeding on more susceptible fish hosts produce larger but not more offspring

Abstract

The reproductive success of female Gnathia marleyi (Crustacea: Isopoda) was examined among individuals from eight species belonging to five families of common Caribbean reef fishes of St. John, US Virgin Islands that differ in susceptibility to G. marleyi infestation. Fish were placed in cages during times of peak gnathiid activity. Gnathiids were recovered from host fishes and reared to adulthood in the laboratory. Ovigerous females were then placed in individual containers until offspring were released. Measures of reproductive success used were the number of hatched zuphea 1 larvae that emerged from the brood pouch, "brood size," and the average total length of newly emerged zuphea larvae, "average z-length." Among the five host fish families tested, females that fed on the two families most susceptible to gnathiid infestation (Haemulidae and Lutjanidae) produced longer larvae than those feeding on the three less susceptible host families. However, there was no significant difference in the number of viable offspring produced. To our knowledge, this is the first study to examine the relationship between the source of the blood meal and any measure of reproductive success in female gnathiid isopods. These findings open the door to future research on potential differences in host blood quality and defense mechanisms that may cause variations in susceptibility to gnathiid among different host fishes.

Nocturnal migration reduces exposure to micropredation in a coral reef fish

“…In the eastern Caribbean Sea, grunts and snappers are more susceptible to gnathiid infestation than are diurnal reef fishes that spend the night on the reef, and more susceptible than other nocturnal species that are active near the reef at night and even feed on gnathiids (Coile and Sikkel 2013). Moreover, gnathiids that feed on grunts and snappers experience fitness benefits over those that feed on some other host species (Coile et al 2014). While the underlying mechanisms are unclear, these findings suggest that high susceptibility to gnathiids is either an underlying evolutionary cause or is a consequence of off-reef migration.…”

“…Although small in size, high gnathiid loads in adult fish can decrease hematocrit (Jones and Grutter 2005), and even cause death (Hayes et al 2011). Their piercing structures can cause tissue damage that can lead to secondary infection (Bunkley-Williams and Williams 1998), and, like terrestrial blood-feeding parasites, they are known or suspected to transmit blood parasites, such as haemogregarine or haemogregarine-like apicomplexans, filarial nematodes, flagellates, fungal structures, and viruses (e.g., Smit and Davies 2004, Davies et al 2009, Curtis et al 2013. More recently, gnathiids have been shown to infect and kill newly-settled juvenile reef fishes (Jones and Grutter 2008, Penfold et al 2008, Grutter et al 2011a, Sun et al 2012, Artim et al 2015.…”

Fish mucus versus parasitic gnathiid isopods as sources of energy and sunscreens for a cleaner fish

“…Although the taxonomic diversity in this study was low (two herbivorous parrotfishes vs. one wrasse and one snapper, both carnivorous), it appears that carnivorous species ''produce'' gnathiids of higher nutritional value. This combined with their lower mucus quality (and potentially their effectiveness as a barrier against gnathiids) has implications for host susceptibility to gnathiids and may explain differences in susceptibility among fishes (Coile and Sikkel 2013), as well as differences in fitness measures of gnathiids that had fed off of different hosts (Nagel and Grutter 2007;Coile et al 2014).…”

Comparison of sampling methodologies and estimation of population parameters for a temporary fish ectoparasite

“…In addition to estimates of overall population densities, an aspect of gnathiid ecology that has been little explored in situ are the various population parameters such as brood size or the time between feeding and ecdysis leading into the next life cycle stage. Such life cycle parameters are typically determined in laboratory culture ( Grutter, 2003 , Smit et al., 2003 , Coile et al., 2014 ).…”