Life history of the Glanville fritillary butterfly in fragmented versus continuous landscapes

Abstract

Habitat loss and fragmentation threaten the long-term viability of innumerable species of plants and animals. At the same time, habitat fragmentation may impose strong natural selection and lead to evolution of life histories with possible consequences for demographic dynamics. The Baltic populations of the Glanville fritillary butterfly (Melitaea cinxia) inhabit regions with highly fragmented habitat (networks of small dry meadows) as well as regions with extensive continuous habitat (calcareous alvar grasslands). Here, we report the results of common garden studies on butterflies originating from two highly fragmented landscapes (FL) in Finland and Sweden and from two continuous landscapes (CL) in Sweden and Estonia, conducted in a large outdoor cage (32 by 26 m) and in the laboratory. We investigated a comprehensive set of 51 life-history traits, including measures of larval growth and development, flight performance, and adult reproductive behavior. Seventeen of the 51 traits showed a significant difference between fragmented versus CL. Most notably, the growth rate of postdiapause larvae and several measures of flight capacity, including flight metabolic rate, were higher in butterflies from fragmented than CL. Females from CL had shorter intervals between consecutive egg clutches and somewhat higher life-time egg production, but shorter longevity, than females from FL. These results are likely to reflect the constant opportunities for oviposition in females living in continuous habitats, while the more dispersive females from FL allocate more resources to dispersal capacity at the cost of egg maturation rate. This study supports theoretical predictions about small population sizes and high rate of population turnover in fragmented habitats selecting for increased rate of dispersal, but the results also indicate that many other life-history traits apart from dispersal are affected by the degree of habitat fragmentation.

Keywords: Dispersal; habitat fragmentation, flight capacity; larval growth; life-history evolution; male mating success; oviposition rate..

Figure 1

(A) Map of the Baltic Sea region with the populations of the Glanville fritillary included in the present study: Åland Islands (ÅL), Uppland coastal region (UP), Öland (ÖL), and Saaremaa (SA). (B) Average monthly temperatures between 1992 and 2001 in ÅL (Blue), UP (Red), and SA (Green). The dashed lines give the average monthly temperatures recorded in ÅL.

Figure 2

Schematic representation of the large outdoor population cage, with the transect surveyed five times a day (dashed line), the potted host plants in the central part of the cage (gray areas), and the grid division of the cage. (A) An inside view of the cage with an assistant monitoring the 200 potted host plants (© A. Jussila). (B) Close-up of the Glanville fritillary butterfly (Melitaea cinxia) (© T. Delahaye).

Figure 3

Larval and pupal development. (A) Weight of the fifth larval instar (mg), (B) larval period (days), (C) pupal weight (mg), and (D) pupal period (days) in Åland (ÅL), Öland (ÖL), Saaremaa (SA), and Uppland (UP) populations. Fragmented landscapes (FL) and continuous landscapes (CL) populations in gray and open boxes, respectively. Heavy horizontal lines represent median values.

Figure 4

Ovipositions. (A) First clutch size, (B) egg weight (mg), (C) lifetime-corrected number of eggs laid (N/day), and (D) time between two consecutive ovipositions (days) in Åland (ÅL), Öland (ÖL), Saaremaa (SA), and Uppland (UP) populations. Fragmented landscape (FL) and continuous landscape (CL) populations in gray and open boxes, respectively. Heavy horizontal lines represent median values.

Figure 5

Flight behavior, metabolism, and morphology. (A) Peak flight metabolic rate (CO₂ production, mL/h, corrected for pupal weight) during forced flight in females and males, (B) Probability of flying in males in the outdoor population cage, (C) body weight allocation to thorax and (D) wing load ratio (mg/mm²) in Åland (ÅL), Öland (ÖL), Saaremaa (SA), and Uppland (UP) populations. Fragmented landscape (FL) and continuous landscape (CL) populations in gray and open boxes. Heavy horizontal lines represent median values.

Figure 6

Principal component analysis of larval and pupal traits. The two principal components PC1 and PC3 from the third principal component analyses in Table 3. Squares for males, circles for females, open symbols for continuous landscapes (CL) and closed symbols for fragmented landscapes (FL). The dashed lines were drawn by eye to ease visualization. CL and FL individuals are well differentiated in females but there is more overlap in males.