Ovigerous Female Amphipods (Gammarus pseudolimnaeus) Face Increased Risks from Vertebrate and Invertebrate Predators

Abstract

We investigated the mortality rates of male and female amphipods resulting from stickleback fish (Culaea inconstans) and dragonfly nymphs (Basiaeschna janata) predation. Both predators consumed significantly more ovigerous female amphipods than non-ovigerous females or males in 24-h trials. Stickleback fish consumed more nonovigerous females than males, whereas dragonflies consumed more males than nonovigerous females. These results were consistent across trials conducted under ambient light-dark regimes and those conducted in the absence of light, although overall mortality rates were highest in light trials. There were no significant differences in the recorded behaviors of the two predators. However, the behavior of ovigerous females differed significantly from that of males and non-ovigerous females, which may help to explain the overall differences in mortality. These results suggest that female amphipods incur a significant cost of increased predation risk associated with maternal care. INTRODUCTIONPredator-prey dynamics are complicated by a range of factors including habitat complexity (e.g., Crowder and Cooper 1982), inter-and intraspecific variation in predator foraging strategies (e.g., Lane 1979, Cothran 2004, and intraspecific variation in prey susceptibility (e.g., Thompson 1975). Differences in predation risk based on sex or other reproductive parameters can impact the ecology of populations and communities, such as the stability of predator-prey dynamics (Newman and Waters 1984, Boukal et al. 2008) and the species composition of prey communities (Crowder and Cooper 1982). Such differences can also impact the evolution of competitive ability (Wellborn 2002), as well as behavior (e.g., mate selection, timing of courtship displays), morphology (e.g., breeding coloration, secondary sexual characteristics), and life history strategies (e.g., reproductive effort, age or size at reproductive maturity) within prey species, as reviewed by Magnhagen (1991).In many freshwater ecosystems, amphipods constitute the largest percentage of macroinvertebrate species richness (MacNeil et al. 1997) and also comprise a substantial component of the diet of economically and ecologically important predators such as salmon and trout (MacNeil et al. 1999). Although the impacts of vertebrate predators on amphipods are most often emphasized, the impacts of invertebrate species, sometimes including predation within feeding guilds or even within the same species, are also very important (MacNeil et al. 1999). Both vertebrate and invertebrate predators have a propensity to specialize on a particular category of amphipod prey, preferring, for example, larger or smaller individuals (e.g., Conlan 1994, Hijlker and Hammer 1994, Wach and Chambers 2007, more mobile individuals (Mathis and Hoback 1997, Boates and Smith 1989), parasitized individuals (e.g., Baldauf et al. 2007, Bakker et al. 1997), or amplexing pairs (e.g., Strong 1973, Ward 1986. The preferences of vertebrate and invertebrate predators can be quite distinc...

Behavioral responses to predation risk in brooding female amphipods (Gammarus pseudolimnaeus)

“…Evidence suggests that brooding female amphipods are more prone to predation by both vertebrate (brook stickleback) and invertebrate (dragonfly nymph) predators (Lewis & Loch Mally 2010). However, those experiments were conducted under laboratory conditions in test containers with no available cover and limited access to conspecifics.…”

“…Female amphipods carry developing eggs and offspring in a ventral brood sac, and there is evidence that ovigerous females face higher risks from both invertebrate and vertebrate predators (Lewis & Loch-Mally 2010) within a restrictive laboratory setting. The authors hypothesized that the higher risk of predation may be due to a reduction in mobility.…”

Population structure of the hadal amphipod Bathycallisoma (Scopelocheirus) schellenbergi in the Kermadec Trench and New Hebrides Trench, SW Pacific

“…It has been suggested that feeding cessation is employed by near-mature females (Bregazzi, 1972) and during incubation to prevent expulsion of the brood (Christiansen et al, 1990;Johnson et al, 2001). Direct observation of shallow water ovigerous Lysianassoid females actively avoiding feeding events also suggests a predator/cannibalism avoidance strategy (Bregazzi, 1972) as ovigerous females can be more susceptible to predation (Lewis and Loch-Mally, 2010). Until ecological sampling at hadal depths can be achieved without the current reliance on baited traps, the ovigerous female proportion of the population cannot be determined.…”

Egg Load Decreases Mobility and Increases Predation Risk in Female Black-Horned Tree Crickets (Oecanthus nigricornis)

“…The physical stress and morphological changes associated with carrying young or eggs may also lead to increased female mortality. Gravid or ovigerous females are often reported to suffer higher predation [17] – [21] . This increased mortality can sometimes be attributed to the physical handicap of females carrying and developing eggs [17] , [22] , [23] .…”