Investigation of leg colour polymorphism in Pterostichus madidus (F.) in relation to climatic factors

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Pudney, K., 2002. Investigation of leg colour polymorphism in Pterostichus madidus (F.) in relation to climatic factors. PhD, Nottingham Trent University.

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Abstract

The ground beetle, Pterostichus madidus (F) (Coleoptera: Carabidae), which is widespread in Britain, is dimorphic for two leg colour forms, red and black. Terrell-Nield (1990a) found an association between leg colour morph proportions and temperature in England and Wales, and proposed that this species could be used as an indicator of climate change. The genetics of leg colour in P. madidus and the mechanism of selection were unknown.

This study investigates the association between the morph frequency distribution of P. madidus and environmental factors from field data collected from a number of regions of England and Wales. Using multiple regression analysis as a diagnostic tool, a positive correlation was found between the red-legged morph and a higher minimum temperature in cooler regions or periods and a lower maximum temperature in warmer regions or periods. Use of monthly climatic data identified winter and spring as the most critical periods. Regardless of the spatial or temporal resolution, the red-legged morph appears to be better adapted to a more equitable climate and is associated with urban and wooded sites; the blacklegged morph is adapted to more extreme temperatures and is associated with intensive agricultural areas. These results could explain why P.madidus is a forest species in Europe, where it is predominantly red-legged, but has extended its range to more northern latitudes and to open country in Britain.

A method for rearing P.madidus larvae under laboratory conditions has been developed. Variables such as pre-reproductive mortality indicate that each developmental stage is adapted to temperatures that would be experienced in the field. A model of the thermal rate to complete development shows that, depending on the month of hatching, 8 to 10 months is required to reach full maturity, adult emergence coinciding over a relatively short period in June. The most critical period for development is from late Instar 3 to emergence. These developmental stages occur from late winter to early summer in the field. This period also produced the strongest coefficient of determination in the multiple regressions. The data sets were too small to identify any difference between the two morphs in their immature stages in terms of their development, growth and survivorship.

Breeding experiments show that the genes coding for red are dominant; this has implications for the modelling of morph frequency change over time.

This study has shown that the mechanism for selection of leg colour is related to temperature but there appear to be many ecotypes among the P. madidus population, each one adapted to different temperature conditions. It is not known whether the leg colour phenotypes are linked to specific ecotypes by pleiotropic genes.

The leg colour morph distribution of P. madidus could be a good indicator of microclimatic conditions on a small spatial scale, which should be of assistance when making decisions about land use. Due to the year-by-year variability in climate and morph proportions, a long time series of 10 to 20 years is needed to identify a correlation between directional changes in morph proportions and climatic factors.

Item Type:

Thesis

Creators:

Pudney, K.

Date:

2002

ISBN:

9781369313840

Identifiers: