Reduced investment in sex as a cost of inducible defence inBrachionus calyciflorus(Rotifera)

Abstract

Summary Inducible defences reduce the probability of prey being killed by their predators. However, these defences are often accompanied by costs. Most studies associated with aquatic communities have focused on the effects of inducible defences on the growth and reproduction of prey species, while their effects on sex investment remain unclear. Brachionus calyciflorus is a common freshwater rotifer that develops a defensive morphology in response to the kairomones released by the predatory rotifer Asplanchna. Some studies have reported that no detectable cost, such as decreased reproductive output, is associated with the spines in B. calyciflorus. Thus, we studied the sex investment (i.e. production of mictic offspring and resting eggs) of B. calyciflorus populations at three Asplanchna kairomone concentrations (0, 10, and 100 Asplanchna L−1) and two food levels (1 and 12 mg C L−1) to evaluate the sex cost of inducible defences. We also evaluated the crowding threshold required to trigger sex investment (i.e. lowest population density at which mictic female is produced) in B. calyciflorus under different kairomone and food treatments. Results showed that (i) the B. calyciflorus population exposed to kairomones produced offspring with elongated posterolateral spines; (ii) the production of mictic offspring and resting eggs decreased in the B. calyciflorus population exposed to kairomones, suggesting an investment trade‐off exists between inducible defence and sex investment; (iii) the decrease in sex investment was higher at the high kairomone concentration than at the low kairomone concentration; (iv) the decrease of sex investment was higher at the low food level than at the high food level; and (v) the crowding threshold of the B. calyciflorus population increased upon exposure to kairomones. The results of this study suggest that the decreased sex investment in defended B. calyciflorus is a form of defence cost. Our findings add to our understanding of the effect of predation on the ecology and evolution of phenotypic plasticity in rotifers.

Predator ontogeny affects expression of inducible defense morphology in rotifers

“…All organisms in the wild optimize their performance and fitness and many do so by adjusting their morphology to reduce their vulnerability to predation. A conspicuous example of predator-avoidance morphology is the induced spine-length polymorphism in many rotifer species (Baker 1979, Hofmann 1983b, Gilbert 2013, 2017, Yin et al 2015b. Such polymorphism has been attributed to temperature (Lindstr€ om and Pejler 1975, Eloranta 1982, Bielañska-Grajner 1995, food availability (Gallagher 1957, Gopko andTelesh 2013), and kairomones from invertebrate predators .…”

“…In addition, the spectacular variance in spine length has also been attributed to differences in predation pressure (Gilbert and Stemberger , Stemberger and Gilbert , Yin et al. ). Most studies have focused on elongation of spines in response to a variety of small, invertebrate predators, such as the predatory rotifer Asplanchna spp.…”

“…Spine length is a phenotypically plastic trait in many rotifer species and changes in spine length have been attributed to different environmental variables, such as temperature (Lindstr€ om and Pejler 1975, Bielañska-Grajner 1995, Gilbert 2011 and food availability (Stemberger 1990, Zagarese andMarinone 1992). In addition, the spectacular variance in spine length has also been attributed to differences in predation pressure , Yin et al 2015b). Most studies have focused on elongation of spines in response to a variety of small, invertebrate predators, such as the predatory rotifer Asplanchna spp.…”

Hidden defensive morphology in rotifers: benefits, costs, and fitness consequences

“…calyciflorus and carnivorous A . brightwellii were obtained from wetting of dried sediment collected from a freshwater pond (39°57′N; 116°21′E) in Beijing, China, following the methods of previous studies 42, 46 . One newly hatched female Brachionus or Asplanchna was isolated and allowed to reproduce parthenogenetically in the COMBO medium 47 enriched with 40 ml L −1 soil water extract 40 (hereafter COMBO).…”

“…The preparation of Asplanchna -conditioned COMBO was described in previous studies 42, 46 . In brief, 100 adult females of A .…”