Chemically-induced plasticity in early life history ofPalaemon argentinus: are chemical alarm cues conserved within palaemonid shrimps?

Abstract

Most aquatic animals use infochemicals from both conspecifics and heterospecifics to assess local predation risks and enhance predator detection. Released substances from injured conspecifics and other species (chemical alarm cues) are reliable cues to indicate an imminent danger in a specific habitat and often mediate the development of inducible defenses. Amphibian and fish embryos have been shown to acquire this information while at the embryonic stage of development, in relation to the developing nervous system and sensory development. With the exception of Daphnia, there is no information on chemically mediated responses to alarm cues in embryos of any crustacean groups. Therefore, we tested whether embryo exposure to chemical cues simulating predation on conspecifics or heterospecifics (closely related, non-coexisting species), or a mixture of both, alters embryonic developmental time, size and morphology of the first larval instar in Palaemon argentinus (Crustacea: Decapoda). Embryonic exposure to chemical alarm cues from conspecifics shortened the embryonic developmental time and elicited larger larvae with a longer rostrum. Rostrum length of the first larval instar changed independently of their size, thus elongated rostra can be considered a defensive feature. Embryonic developmental time was not altered by chemical alarm cues from either heterospecifics or the mixed cues treatment; however, exposure to these cues resulted in larger larvae compared with the control group. Chemically induced morphological plasticity in larvae in response to alarm cues from con-and heterospecifics suggests that such cues are conserved in palaemonids shrimps, providing embryos with an innate recognition of heterospecific alarm cues as predicted by the phylogenetic relatedness hypothesis.

Innate responses to con‐ and heterospecific alarm chemicals in juveniles of a freshwater shrimp

“…All the three stimuli were applied every single day during the whole embryonic development, that is, immediately after egg spawning until the day before hatching (Fig. 1c, conditioning period; for further details, see Ituarte et al., 2019). Experimental units (=ovigerous females) were kept in individual plastic and opaque containers (1 L) filled with 800 mL of tap water (water depth 10 cm).…”

“…We collected females almost ready to spawn (fully developed ovaries are visible through the thin transparent exoskeleton) and adult males of the freshwater shrimp P. argentinus from the littoral zone of Los Padres Lake, Buenos Aires Province, Argentina (Pampa Plain, 37°55 0 S, 57°43 0 W) (further details in Ituarte et al, 2019). Shrimps were collected using a hand net (45 cm width, 30 cm deep, and 1 mm mesh size), and were kept in a laboratory aquarium (30 9 30 cm, 50 cm high) filled with tap water with constant aeration.…”

“…alarm cues; diet cues, and most predator‐specific odors) is still unknown (Mitchell et al., 2017; Schoeppner & Relyea, 2005; Wisenden, 2003). Exploring the specificity of the responses can shed some light on the degree of conservation of molecules acting as an alarm (Ituarte et al., 2019).…”

Chemical Cues Released by Predators’ Consumption of Heterospecific Prey Alter the Embryogenesis of Zebrafish

“…Though previous research on predator-prey interaction has primarily examined adult individuals, recent studies have demonstrated that embryos also respond to predation [3]. Embryos can modify their morphological and behavioral characteristics by responding to external cues prior to hatching [4,5]. Therefore, embryos should not be viewed as "works-in-progress" following a pre-programmed developmental pathway but rather as viable organisms with plasticity that can adapt to dynamic contexts.…”