An experimental test of mate choice for red carotenoid coloration in the marine copepod Tigriopus californicus

Abstract

Colorful ornaments are hypothesized to have evolved in response to sexual selection for honest signals of individual quality that provide information about potential mates. Red carotenoid coloration is common in diverse groups, and in some vertebrate taxa, red coloration is a sexually selected trait whereby mates with the reddest ornaments are preferred. Despite being widespread among invertebrates, whether red carotenoid coloration is assessed during mate choice in these taxa is unclear.The marine copepod Tigriopus californicus displays red coloration from the accumulation of the carotenoid astaxanthin. Previous research on copepods has shown that astaxanthin provides protection from UV radiation and xenobiotic exposure and that carotenoid production is sensitive to external stressors. Because of the condition dependency of the red coloration, we hypothesized that Tigriopus would use it as a criterion during mate choice. To test this hypothesis, we conducted trials in which males chose between females that were wild-type red (carotenoid-rich algae diet) or white (carotenoid-deficient yeast diet). To control for dietary differences and to isolate the effect of carotenoid coloration, we also presented males with restored-red females fed a carotenoid-supplemented yeast diet. We found that wild-type red females were weakly preferred over white females. After controlling for diet, however, we found that restored-red females were avoided. Our observations do not support the hypothesis that male copepods prefer the carotenoid coloration of females during mate choice. We hypothesize that algal-derived compounds other than carotenoids play a role in mate choice. Red coloration in copepods appears to be a condition-dependent trait that is not assessed during mating. K E Y W O R D Sastaxanthin, crustacean, mate guarding, ornamentation, sexual selection, zooplankton

Evidence for hybrid breakdown in production of red carotenoids in the marine invertebrate Tigriopus californicus

“…It could be that the malnourishing yeast diet limited variation in offspring development, slowing all lines and changing the relationship between offspring development and astaxanthin bioconversion. These results could support the idea that astaxanthin pigmentation is fundamentally tied to individual condition [ 2 , 24 ], even in systems that do not experience sexual selection on carotenoid coloration [ 49 ].…”

“…Prior to the start of the experiment, RIL copepods were switched to a diet of ground nutritional yeast until they became clear in color and deficient of both carotenoid precursors and the primary red carotenoid, astaxanthin [ 9 , 49 ]. To test carotenoid bioconversion rate, carotenoid-deficient copepods were provided Tetraselmis chuii algae ad libitum for 7 days to mimic the copepod’s natural diet of photosynthetic algae rich with carotenoid precursors [ 50 ].…”

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“…In the yeast-only inbred lines, we found that offspring from all lines developed at similar rates (S3 Fig); however, in the reciprocal cross between SD and SCN fed algae, we found that development rate was significantly longer in hybrids by the third generation (S14C Fig) . We have frequently observed longer development rates in laboratory cultures fed yeast-only diets, and in the data in this study we also observed that parental copepods fed yeast only produced offspring with longer development rates on average compared to parental copepods fed algae (S1E Fig) . It could be that the malnourishing yeast diet limited variation in offspring development, slowing all lines and changing the relationship between offspring development and astaxanthin bioconversion. These results could support the idea that astaxanthin pigmentation is fundamentally tied to individual condition [2,24], even in systems that do not experience sexual selection on carotenoid coloration [49].…”

A combination of red structural and pigmentary coloration in the eyespot of a copepod

“…We hypothesize that copepods combine both astaxanthin and structures in a similar manner to jumping spiders, which is why their eyespots appear non-iridescent under light microscopy. Jumping spiders and other bright red animals like house finches ( Haemorhous mexicanus ) produce red colour for display, but the red eyespot of a copepod is unlikely involved in sexual signalling [21,46,47]. Instead, the bright red eyespot colour, that is present in many other organisms as well, may have a functional role.…”