How the ladybird got its spots: effects of resource limitation on the honesty of aposematic signals

Abstract

Summary1. Prey species often possess defences (e.g. toxins) coupled with warning signals (i.e. aposematism). There is growing evidence that the expression of aposematic signals often varies within species and correlates with the strength of chemical defences. This has led to the speculation that such signals may be 'honest', with signal reliability ensured by the costliness of producing or maintaining aposematic traits. 2. We reared larval seven-spot ladybirds (Coccinella septempunctata) on a Low or High aphid diet and measured the effects on warning signal expression (elytral carotenoid pigmentation, conspicuousness, spot size), levels of defensive alkaloids (precoccinelline, coccinelline), and relationships between these traits. 3. High-diet individuals had greater total precoccinelline levels, and elytra carotenoid concentrations at adulthood which was detectable to a typical avian predator. However, larval diet did not significantly affect adult body mass or size, spot size or coccinelline levels. 4. Elytra carotenoid concentrations correlated positively with total precoccinelline levels in both diet groups and sexes. However, the relationship between elytra carotenoid concentrations and total levels of coccinelline depended on sex: in both diet groups, elytra carotenoids and coccinelline levels were positively correlated in females, but negatively correlated in males. Spot size and coccinelline levels correlated positively in Low-diet individuals, but negatively in High-diet individuals. 5. These results point to physiological linkages between components of aposematism, which are modulated by resource (i.e. food) availability and affect the honesty of signals. Developmental diet, but also sex, influenced the relationships between signals and toxin levels. Ladybirds are sexually size dimorphic, and thus in comparison with males, females may be more susceptible to resource limitation and more likely to be honest signallers.

Not attackable or not crackable—How pre‐ and post‐attack defenses with different competition costs affect prey coexistence and population dynamics

“…Accordingly, predator and defended prey may evolve toward avoiding interactions with each other which would mean that being not attacked is the prevailing defense strategy. This reasoning is supported by the observation that many defended prey species show warning signals to deter the predator from attacking them (Blount et al., 2012; Stevens & Ruxton, 2012) and that predators often show behavioral changes to avoid defended prey species (White et al., 2011; Xu, Nielsen, & Kiørboe, 2018). However, not attacking defended prey species implies a higher grazing pressure on undefended prey species which may reduce their population densities leading to the dominance of defended prey species.…”

Influences of geographic differentiation in the forewing warning signal of the wood tiger moth in Alaska

“…Some of the species found to have geographically varying warning signals include Neotropical Heliconius butterflies (Brown & Benson 1974, Brower 1996, Mallet 2010, ladybird beetles (Creed 1966, Brakefield 1985, Dolenská et al 2009, Blount et al 2012, monarch butterflies (Brower 1958, Davis et al 2005, Davis et al 2012, newts (Mochida 2009, Mochida 2011, poison frogs (Daly & Myers 1967, Savage 1968, Summers et al 2003, Wang & Summers 2010, Wang 2011, Rudh et al 2011, Maan & Cummings 2012, Willink et al 2013, RichardsZawacki et al 2013, Hegna et al 2013b), velvet ants (Wilson et al 2012), alpine leaf beetles (Borer et al 2010), and bumble bees (Plowright & Owen 1980). Interestingly, some aposematic species appear to switch between aposematic and cryptic strategies across their distributions.…”

Color contrast and stability as key elements for effective warning signals

“…Ladybird coloration varies greatly across species, and there are also several cases of within-species color polymorphisms (Osawa and Nishida, 1992;de Jong and Brakefield, 1998). In addition, ladybirds have toxic chemicals that are produced endogenously (Dixon, 2000;Bezzerides et al, 2007;Blount et al, 2012). These chemicals are correlated with color properties in some species (Blount et al, 2012).…”

“…Several studies have suggested that ladybird color patterns, and overall appearance, are important for predator detection (Marples et al, 1989(Marples et al, , 1994Dolenská et al, 2009). However, only recently Blount et al (2012) considered the actual role of avian visual sensitivity in their results. Ladybird beetles are widely distributed and abundant in the United Kingdom, and the diversity of their coloration is impressive.…”

“…In addition, ladybirds have toxic chemicals that are produced endogenously (Dixon, 2000;Bezzerides et al, 2007;Blount et al, 2012). These chemicals are correlated with color properties in some species (Blount et al, 2012). Several studies have suggested that ladybird color patterns, and overall appearance, are important for predator detection (Marples et al, 1989(Marples et al, , 1994Dolenská et al, 2009).…”