Mating marks on museum specimens reveal breeding patterns in species of Pterostichus Bonelli (Carabidae, Pterostichini).

Kipling Will,Patina Mendez

doi:10.3897/bdj.9.e70897

Abstract

We found distinct and consistently placed, species- and sex-specific abrasions of the cuticle on museum specimens of 14 species of the Pterostichus Bonelli, 1810 (Carabidae, Pterostichini) subgenusHypherpes Chaudoir, 1838. We deduced that these marks are generated during mating and, therefore, can be used to distinguish between preserved specimens of beetles that had previously mated at the time of capture and those that had not mated. In addition to describing and detailing the occurrence of the marks and providing evidence that they are the result of mating, we demonstrate their utility for inferring life history using a museum voucher collection. By scoring these indications of mating from pinned specimens, we describe life cycle patterns in two similar, relatively closely related and sympatric species of the subgenus Hypherpes, P.vicinus Mannerheim, 1843 and P.californicus (Dejean, 1828). Both were sampled during a pitfall trap study in Contra Costa, California, USA from 2014–2019 and deposited in the Essig Museum of Entomology, UC Berkeley. Both species had very low adult activity through the drought and end of drought period prior to the spring of 2017 and are significantly more abundant in the post-drought period. Based on mating marks, both species responded to accumulated precipitation ending the drought by the emergence of an active, mostly unmated cohort of adults. The spring activity peak, following the end of the drought, was dominated by unmarked and presumably unmated beetles, but samples from subsequent springs included a nearly equal mix of beetles showing mating marks and apparently unmated beetles. The beetle activity appears to correspond more with the accumulated rainfall of the preceding rainy season than with the rains of the sample year. Beetles sampled in autumn and winter (rainy season) predominantly show mating marks. The occurrence throughout the year of beetles that are marked as having mated is consistent with iteroparous beetles with a lifespan of more than one year and also consistent with dynamic phenotypic polyvariance in which the adult activity period is synchronised by adjusting development time. The dominant pattern fits with a life cycle that is typically annual univoltine, or possibly biennial semivoltine in dry years, rainy season breeding (autumn-winter) iteroparous, with adult summer aestivation and possibly facultative larval hibernation. However, unmarked and so apparently unmated individuals and teneral adults were captured during peak activity periods regardless of the season, suggesting that either the beetles diapause as teneral adults that then complete development and become active at various points during the year and/or there are multiple periods of breeding and oviposition each year in at least some portion of the population.

Highlights

A total of 42 specimens that have been provisionally identified as P. protensiformis were sampled in winter and early spring periods, and like P. angustus were active during the cooler, short-day, rainy season
Within our small sample of taxa, we found both of the sister species pair (Will and Gill 2008) P. serripes and P. tarsalis have mating marks
The mating marks we report here for 14 species of Hypherpes represent the only occurrences of this particular phenomenon of external cuticular abrasions revealing mating status known for insects

Summary

Introduction

There is a wealth of publications on life-history traits of carabids, albeit based almost entirely on species from middle-and high-latitude temperate regions that experience cool to cold winters and significant precipitation throughout most of the year (e.g., Kaufmann 1971, Bousquet 1986, Castro et al 2014, Lindroth 1985, Lindroth 1986, see various summary publications, den Boer and van Dijk 1998, Thiele 1977, Matalin 2007, Nolte et al 2019, Kotze et al 2011, Homburg et al 2013) with a few exceptions (e.g., Paarmann 1970, Paarmann 1973, Paarmann 1974). Other publications on North American pterostichines propose breeding patterns based on adult activity, the occurrence of teneral individuals, or observations of apparent mating in the field (e.g., Bergdahl and Kavanaugh 2011, Bousquet 1999) These publications use the terms “autumn breeder” and “spring breeder,” a system introduced by Larsson (1939) to describe carabid life cycles. In this system spring breeders have an adult activity peak in spring when mating occurs, oviposition in late spring and summer, larval development in summer, a second adult activity peak in autumn when feeding but not mating occurs, and adults hibernate in winter. Autumn breeders have a single adult activity peak in summer into autumn when mating occurs, oviposition happens in late summer to early autumn, larval development and hibernation occur through the following spring

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Discussion

Conclusion