Chemical defence effective against multiple enemies: Does the response to conspecifics alleviate the response to predators?

Abstract

1. Animals living in groups with high conspecific densities typically decrease their level of plastic anti-predatory defence because its benefits diminish with reduced per capita predation risk (a benefit of aggregation), whereas its costs increase due to intensifying competition and increased infection risk. Furthermore, phenotypic responses that provide protection from predators are also often disadvantageous against competitors and infections.2. Such a trade-off may be absent when the same phenotype provides an effective defence against both predators and competitors, as is the case with some chemical defences. For such multifunctional defensive traits, both predation risk and high conspecific density are expected to increase defence expression while exposure to both predators and conspecifics may result in non-additive effects whereby the defence level induced by two enemies is lower than the sum of responses induced by either of them alone.3. We tested this theoretical prediction by studying the effects of multiple enemies on chemical defence in a vertebrate animal. We investigated patterns of change in toxin production of common toad Bufo bufo tadpoles following exposure to different conspecific densities and the simultaneous presence or absence of chemical cues on predation risk. 4. We found that tadpoles significantly increased their production of bufadienolide toxins in response to high tadpole density, as well as to predation risk when tadpole density was low. Although the response in bufadienolide production to predation risk was not significant at high tadpole density, the magnitude of anti-predatory response did not differ significantly between low and high tadpole densities.5. These results show that toad tadpoles adjust their chemical defence to conspecific density and to predation risk simultaneously, and these two effects are more likely additive than non-additive, at least within the range of densities and predation-risk levels studied here. Nevertheless, the trend we found suggests that toxin levels induced by very high conspecific density might weaken the chemical response to predators, which is relevant for the evolutionary ecology of chemical defences, as well as for the conservation of fauna impacted by toxic invaders. | 2295Functional Ecology ÜVEGES Et al.

Metamorphic common toads keep chytrid infection under control, but at a cost

“…Although we do not explicitly know the ultimate cause and physiological mechanisms behind the observed decrease in TBQ, this might be the consequence or cost of Bd infection due to the disruption of normal skin function or trade‐offs with other fitness traits which are important for battling the fungus. Nonetheless, a weakened chemical defense is likely to lower survival probabilities and thereby the fitness of affected individuals, by rendering them more vulnerable to pathogens, parasites, competition, and predators (Barnhart et al., 2017; Bókony et al., 2018; Cunha Filho et al., 2005; Hayes et al., 2009; Toledo & Jared, 1995; Üveges et al., 2021).…”

“…On 24 April, which was between 4 and 8 days after tadpoles reached the free‐swimming stage (development stage 25 according to Gosner, 1960), we placed 55 tadpoles from each family into outdoor mesocosms (150 L plastic tubs, 57 × 39 × 28 cm), so that each tub only contained tadpoles from one family. Mesocosms provided semi‐natural conditions for tadpoles: They were filled with 130 L aged tap water and contained 40 g dried beech ( Fagus sylvatica ) leaves and 1 L pond water, providing nutrients and refuge (e.g., Van Buskirk, 2012; Mikó et al., 2015; Üveges et al., 2021). When the first individuals reached developmental stage 42 (emergence of forelimbs, start of metamorphosis), we monitored mesocosms daily, captured metamorphs, and placed them into semitransparent, 45‐L plastic boxes (one box for each mesocosm) equipped with a perforated lid.…”

“…Bufadienolides do not only deter various predators (Hayes et al., 2009; Toledo & Jared, 1995) but may also show antimicrobial, antiprotozoal, and antifungal activity, providing some level of protection against pathogens and parasites, including Bd (Barnhart et al., 2017; Cunha Filho et al., 2005; Rodriguez et al., 2020, 2021; Tempone et al., 2008). Bufadienolide synthesis is a flexible trait, which is influenced by anthropogenic habitat change and pollution (Bókony et al., 2017, 2019), the presence of predators or competitors (Benard & Fordyce, 2003; Bókony et al., 2016, 2018; Hagman et al., 2009; Üveges et al., 2017, 2021), food availability (Üveges et al., 2017), and the age of individuals (Ujszegi et al., 2017, 2021; Üveges et al., 2017). However, little is known about the effects of pathogens on inducible bufadienolide synthesis.…”

Does the Glucocorticoid Stress Response Make Toads More Toxic? An Experimental Study on the Regulation of Bufadienolide Toxin Synthesis

“…2019 ), high conspecific density ( Bókony et al. 2018 ; Üveges et al. 2021 ), reduced food availability ( Üveges et al.…”

Effect of victim relatedness on cannibalistic behaviour of ladybird beetle,Menochilus sexmaculatusFabricius (Coleoptera: Coccinellidae)

“…In animal taxa, where parents frequently deposit eggs in clusters in a spatially constrained area, the chances of increased levels of competition between the conspecifics is high (Singh et al ., 2019; Zaviezo et al ., 2019; Uveges et al ., 2021). In such a scenario, discrimination between related individuals becomes essential.…”