Multiple inducers in aquatic foodwebs: Counter-measures and vulnerability to exotics

Abstract

Do aquatic predator and prey species interact strongly enough to foster specialized coevolutionary feedbacks, or are interactions strongly asymmetrical, with prey species responding much more strongly and to multiple threats? Here we utilize prey induction to measure the strength of interactions around a reciprocal "arms race" candidate (Epischura-Bosmina). When prey (Bosmina) are transferred from predator-poor to predator-rich environments, defensive spines increase in length to achieve a plateau after 12-16 d (1-2 generations). Spine lengths are reversible with predator addition and removal, confirming developmental induction as the major short-term response. Laboratory assays reveal major geographic variation, implying active evolution. Responses range from almost no spine elongation where Epischura is historically absent (Europe), to major elongation where the predator and prey are in prolonged contact (Laurentian Great Lakes). Tradeoffs (i.e., loss of competitive ability) can be related to spine lengths of the prey species. However, induction is not exclusive to Epischura, as a collection of invertebrate predators also induce spine elongation. Bosmina responses to individual predator species are different, implying active recognition of multiple predation threats in nature. The absence of induction responses to some exotics (e.g., Bythotrephes) may help explain disproportionate food web impacts. Both revelations underscore the importance of ongoing evolution in aquatic communities.

A plague of waterfleas (Bythotrephes): impacts on microcrustacean community structure, seasonal biomass, and secondary production in a large inland-lake complex

“…More details on experimental design, responses of Bosmina spp. from numerous geographic locations, and reactions to a larger variety of predators, can be found in Kerfoot and Savage (2016).…”

“…Previous studies have established that the distribution of spine lengths closely resemble the normal distribution, although a positive relationship between the standard deviation and mean reveals an underlying log normal distribution (Kerfoot 1988). Moreover, spine length often remains nearly constant over body size, simplifying statistical comparisons (Kerfoot 1987;Kerfoot and McNaught 2010;Kerfoot and Savage 2016). Here mean spine elongation (predator treatment spine length-control length) from multiple ''split-culture'' experiments were compared using t tests.…”

Predator-specific reversibility of morphological defenses inDaphnia barbata

“…Nearly all organisms are exposed to predation, whether predation sensu strictu, grazing or parasitism (Begon et al, 2005). As a result, inducible defenses are extremely widespread in taxa ranging from bacteria (Fiałkowska and Pajdak-Stós, 1997) to protozoa (Kuhlmann et al, 1999), plants (Mcnaughton and Tarrants, 1983;Maleck and Dietrich, 1999;Franceschi et al, 2005;Mithöfer and Boland, 2012) and animals (Lass and Spaak, 2003;Kishida and Nishimura, 2005;Touchon and Warkentin, 2008;Kishida et al, 2009;Ángeles Esteban, 2012;Gómez and Kehr, 2012;Miner et al, 2013;Kerfoot and Savage, 2016). However, when predators disappear or change an inducible defense that once held a benefit, this could then lead to a disadvantage and be costly.…”

Long‐term survey data reveal large predator and temperature effects on population growth of multiple zooplankton species

“…This exercise yields that D. mendotae , B. longirostris , and D. thomasi densities would respectively be reduced by 52%, 80%, and 65% at mean B. longimanus densities (averaged across dates when each species occurs above the threshold density) and 71%, 96%, and 90% at maximum B. longimanus densities over 30 d. Clearly, these are very large predicted reductions in zooplankton densities that would be expected to affect zooplankton composition and influence other organisms (e.g., fish) that prey on zooplankton. Effects of B. longimanus may be particularly large, as defenses may be stronger against native predators (e.g., E. lacustris , Leptodora kindtii , and L. macrurus ) than exotics like B. longimanus (Kerfoot and Savage ). Variation in B. longimanus densities over time (e.g., due to declines in predation on B. longimanus from planktivorous fish after the quagga mussel expansion, Vanderploeg et al ) may thus have large consequences for other components of the food web.…”