Differences in winter cold hardiness support the geographic range disjunction of Neophasia menapia and Neophasia terlooii (Lepidoptera: Pieridae)

Authors: Halbritter, Dale; TEETS, NICHOLAS - University Of Kentucky; WILLIAMS, CAROLINE - University Of California; DANIELS, JARET - Florida Museum Of Natural History

Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2018
Publication Date: 5/1/2018
Citation: Halbritter, D.A., Teets, N., Williams, C., Daniels, J. 2018. Differences in winter cold hardiness support the geographic range disjunction of Neophasia menapia and Neophasia terlooii (Lepidoptera: Pieridae). Journal of Insect Physiology. 107:204-211. https://doi.org/10.1016/j.jinsphys.2018.03.005.
DOI: https://doi.org/10.1016/j.jinsphys.2018.03.005

Interpretive Summary: Rapid climate change can have strong effects on organisms in isolated habitats, and organisms at their geographic range boundaries are particularly sensitive to climate change. Insects are physiologically dependent on ambient temperatures and are therefore often geographically limited by extremes in ambient temperatures. Here, we compared the cold hardiness strategies employed by the overwintering egg stages of two geographically widespread butterflies, Neophasia menapia and N. terlooii , at the near-contact zone of their range boundaries in Arizona, USA. Temperatures at which eggs froze and at which point mortality occurred were compared between the species. Neophasia menapia eggs froze at a significantly lower temperature (-29.0 ± 0.6°C) than eggs of N. terlooii (-21.8 ± 0.7°C). Both species could survive temperatures that neared their respective freezing points. Exposure time to sub-freezing temperatures did not significantly reduce N. menapia hatching, but N. terlooii eggs experienced greater mortality at sub-freezing temperatures during longer exposure times. These results, coupled with an analysis of microclimate data, indicate that colder winters in northern Arizona may contribute to the northern range limit for N. terlooii. Furthermore, careful analysis of historical weather data indicates that mortality from freezing is unlikely in southern Arizona but possible in northern Arizona. Movements of Neophasia range boundaries should be monitored as potential biological responses to climate change.

Technical Abstract: Predicting how rapid climate change will affect terrestrial biota depends on a thorough understanding of an organism's biology and evolutionary history. Organisms at their range boundaries are particularly sensitive to climate change. As predominantly terrestrial poikilotherms, insects are often geographically limited by extremes in ambient temperatures. Here, we compared the cold hardiness strategies of two geographically widespread butterflies, the pine white, Neophasia menapia, and the Mexican pine white, N. terlooii (Lepidoptera: Pieridae), at the near-contact zone of their range boundaries. Eggs are laid on pine needles in their mountain habitats and are exposed to harsh winter conditions. Eggs were collected from wild-caught butterflies, and we determined the supercooling point (SCP) and lower lethal temperature (LLT) of overwintering eggs. The SCP of Neophasia menapia eggs (-29.0 ± 0.6°C) was significantly lower than that of N. terlooii eggs (-21.8 ± 0.7°C). Both species were freeze-intolerant and capable of surviving down to their respective SCPs. Exposure time to low temperature did not have a significant effect on N. menapia hatching, but N. terlooii eggs experienced greater mortality at sub-freezing temperatures during longer exposure times. Our results, coupled with an analysis of microclimate data, indicate that colder winters in northern Arizona may contribute to the northern range limit for N. terlooii. Furthermore, careful analysis of historical weather data indicates that mortality from freezing is unlikely in southern Arizona but possible in northern Arizona. We propose that movements of Neophasia range boundaries should be monitored as potential biological responses to climate change.