# Estimation of Selection Intensity Against Dark Color Forms of the Spittlebug Philaenus spumarius (L.) in a Warming Climate

## TL;DR

Warmer temperatures in Minnesota led to a decline in dark-colored meadow spittlebugs, showing climate change affects natural selection.

## Contribution

Quantifies the selection intensity against dark spittlebug forms over 47 years of climate warming.

## Key findings

- Dark spittlebug forms declined by a third as temperatures rose by 2.7°C over 47 years.
- Selection coefficients estimated at 0.0125 and 0.0218, indicating a 1-2% annual disadvantage for dark forms.
- The spittlebug's role as a vector for plant pathogens highlights its agricultural significance.

## Abstract

When the climate warms, natural selection may work against previously favored insect characteristics. Spittlebugs are sapsucking insects that live on plants. In the meadow spittlebug, the meadow spittlebug, a species found in Eurasia, North America and New Zealand, individuals exhibit one of several distinct color patterns determined by alternative forms of a single gene. Some have a dark coloration that absorbs more sunlight, giving them an advantage in cold environments, where dark forms tend to be more common. Over a 47-year interval in Northern Minnesota, USA, the mean temperature increased by 2.7 °C, while the proportion of genetically determined dark-color forms dropped by about a third, which is believed to be the result of selection against dark forms. This analysis estimates the intensity of natural selection against the dark forms, providing a quantitative measure of long-term biological change attributable to climate warming. The biology of the meadow spittlebug is of particular agricultural interest because it can infect plants, such as olive trees and grapevines, with a bacterium that causes serious diseases.

Climate warming puts new selective pressures on natural populations, but there are few quantitative measurements of selection in natural populations over protracted time periods. Observations made at the beginning and end ofa 47-year cumulative increase of 2.7 °C in the mean September temperature in Northern Minnesota, USA, permit quantitative estimation of selection against a suite of alleles at a single locus determining the expressionof dark color forms in populations of the meadow spittlebug, Philaenus spumarius (L.) (Hemiptera: Cercopoidea: Aphrophoridae). Alternative methods of estimation of the selection coefficient s, a measure of the intensity of selection, produce values of s = 0.0125 and 0.0218, respectively, corresponding to a disadvantage of about one to two percent per year or, since P. spumarius is univoltine, per round of selection. The existence of a locus under selection presents an opportunity for molecular localization and characterization of the genetic locus determining color form. Philaenus spumarius is of particular interest in Europe, as it is the major local vector of the bacterial plant pathogen Xylella fastidiosa.