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Revisiting geographic variation in melanism of monarch butterfly larvae in North America using iNaturalist photos.

Authors :
Davis, Andrew K.
Nibbelink, Nate
Deneka, Christian J.
Source :
Journal of Thermal Biology. Dec2022, Vol. 110, pN.PAG-N.PAG. 1p.
Publication Year :
2022

Abstract

Monarch butterflies in North America have an exceptionally large breeding distribution, occupying regions west of the Rocky Mountains and throughout the eastern seaboard. An experimental study conducted 17 years ago and published in this journal appeared to show that western monarch larvae tend to have smaller black stripes than those from eastern parents, which at the time was thought to be an adaptation to higher solar exposure in California. Here, we revisit this question by measuring melanism of eastern and western larvae from online photographs submitted to iNaturalist by members of the public. We downloaded over 500 photos of larvae from 10 different states (4 in the west, 6 in the east) and used image analysis to quantify the size of each larva's black stripes (% of surface covered by black). We compared average melanism level between east and west, while also accounting for temperature (at the photo location), seasonal effects, and latitude. Results showed larvae tended to be darker with lower development temperatures, and later in the season, though there was no significant difference between eastern and western larvae in their degree of melanism. It is not yet clear why findings here were different from the prior experimental study. Also, the wild larvae appeared to be notably lighter in color than the captive-reared larvae of the original study, suggesting that the captive environment does not truly replicate the developmental experience of wild larvae, at least in terms of cuticular development. Thus, if there truly are innate tendencies for western larvae to differ (morphologically) from eastern, they are not observable in nature. • Monarch butterflies in North America were once thought to have two distinct eastern and western populations. • Early laboratory work published in this journal showed western larvae were lighter in color than eastern. • Melanism levels of 500+ online photos of wild larvae showed no difference between western and eastern subpopulation larvae. • Monarch larvae tend to be darker with lower temperatures, and, later in the season. • Findings are consistent with more recent evidence for a single population in North America. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
03064565
Volume :
110
Database :
Academic Search Index
Journal :
Journal of Thermal Biology
Publication Type :
Academic Journal
Accession number :
160538610
Full Text :
https://doi.org/10.1016/j.jtherbio.2022.103374