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Efectos de la consanguinidad en la morfologa y reproduccin en Morpho peleides (Nymphalidae)
Effects of inbreeding on morphology and reproduction in Morpho peleides (Nymphalidae)
Populations limited in dispersal ability have higher rates of inbreeding and lower gene flow than large, well-connected populations. Inbreeding depression causes some morphological characteristics to change
predictably in butterfly populations, and these may therefore be indicators of overall fitness. I examined differences in body size and symmetry between wild-caught Morpho peleides individuals and individuals from an inbred population to observe the effects of inbreeding on morphological characteristics. Inbred butterflies had lower average forewing length than wild ones, and thus lower overall body size, but there were no detectable differences in asymmetry. Body size was positively correlated with body mass, and
body mass was found to be positively correlated with fecundity, which may have serious consequences for establishment of future generations in inbreeding butterfly populations. This finding is an example of how alteration of a morphological trait can constrain an important life history trait, fecundity.
Las poblaciones con limitacin en la habilidad de dispersin tienen altas tasas de endogamia y un bajo flujo de genes comparado con las poblaciones conectadas. La depresin por endogamia causa que algunas caractersticas morfolgicas cambien especialmente en poblaciones de mariposas, y estas pueden ser indicadoras del xito reproductivo. Examin las diferencias en el tamao corporal y la simetra entre los individuos capturados en el ambiente natural y de una poblacin endogmica de Morpho peleides para observar el efecto de la endogamia en las caractersticas morfolgicas. Las mariposas endogmicas tienen un menor tamao en las alas anteriores que las mariposas silvestres y as un menor tamao corporal, pero no hubo diferencias detectables en la simetra. El tamao corporal est correlacionado positivamente con la masa corporal y la masa corporal est positivamente correlacionada con la fecundidad, lo cual puede tener serias consecuencias para el establecimiento de las futuras poblaciones endogmicas de mariposas. Este hallazgo es un ejemplo de cmo la alteracin de un rasgo morfolgico puede influenciar un rasgo importante como la fecundidad.
Text in English.
Monteverde Biological Station (Costa Rica)
Estacin Biolgica de Monteverde (Costa Rica)
Tropical Ecology Fall 2009
Ecologa Tropical Otoo 2009
t Monteverde Institute : Tropical Ecology
Effects of inbreeding on morphology and reproduction in Morpho peleides (Nymphalidae) Brittany Pahnke Department of Zoology, University of Wisconsin Madison ABSTRACT Populations limited in dispersal ability have higher rates of inbreeding and lower ge ne flow than large, well connected populations. Inbreeding depression causes some morphological characteristics to change predictably in butterfly populations, and these may therefore be indicators of overall fitness. I examined differences in body size an d symmetry between wild caught Morpho peleides individuals and individuals from an inbred population to observe the effects of inbreeding on morphological characteristics. Inbred butterflies had lower average forewing length than wild ones, and thus lower overall body size, but there were no detectable differences in asymmetry. Body size was positively correlated with body mass, and body mass was found to be positively correlated with fecundity, which may have serious consequences for establishment of futur e generations in inbreeding butterfly populations. This finding is an example of how alteration of a morphological trait can constrain an important life history trait, fecundity. RESUMEN Poblaciones con limitaciÃ³n en la habilidad de dispersi Ã³n tienen alt as tasas de endogamia y un bajo flujo de genes comparado con poblaciones conectadas. DepresiÃ³n por endogamia causa que algunas caracterÃsticas morfolÃ³gicas cambien especialmente en poblaciones de mariposas, y estas pueden ser indicadoras del Ã©xito reprodu ctivo. ExaminÃ© diferencias en el tamaÃ±o corporal y simetrÃa entre individuos capturados en ambiente natural y de una poblaciÃ³n endogÃ¡mica de Morpho peleides para observar el efecto de la endogamia en las caracterÃsticas morfolÃ³gicas. Mariposas endogÃ¡mica s tienen un menor tamaÃ±o en las alas anteriores que las mariposas silvestres y asÃ un menor tamaÃ±o corporal tambiÃ©n, pero no hubo diferencias detectables en simetrÃa. El tamaÃ±o corporal estÃ¡ correlacionado positivamente con la masa corporal y la masa corp oral estÃ¡ positivamente correlacionada con la fecundidad, lo cual puede tener serias consecuencias para el establecimiento de futuras en poblaciones endogÃ¡micas de mariposas. Estos resultados es un ejemplo de cÃ³mo la alteraciÃ³n de un rasgo morfolÃ³gico pue de influenciar un rasgo importante como la fecundidad. INTRODUCTION Inbreeding depression is the reduction in fitness of progeny due to mating between related individuals (Clarke 1995). Populations that are small or isolated are often limited in dispersa l ability and, therefore, have higher rates of inbreeding and lower gene flow than large, well connected populations (Vandewoestijne et al. 2008). Two mechanisms responsible for inbreeding depression are increased expression of deleterious recessive allele s and decreased additive genetic variance (Clarke 1995, DeRose & Roff 1999, Saccheri et al. 1998). Charlesworth and Charlesworth (1987) pointed out that even deleterious alleles with small effects can contribute significantly to inbreeding depression. Thus , when comparing selfed to outcrossed progeny, large reductions in fitness can be expected if the level of inbreeding decline is high.
Inbreeding depression in butterflies has been studied extensively in captive as well as wild populations ( Saccheri et al . 1998, Saccheri et al. 2000, Joron & Brakefield 2003, Casula et al. 2004, Fischer 2006, Vandewoestijne 2008 ). Fischer (2006) compared Bicyclus anynana butterflies selected for large or small egg size against unselected butterflies. The resulting inbreedin g reduced mating success, even though mating success had nothing to do with the selected trait (Fischer 2006). A different study, involving intentionally inbred B. anynana lines, produced a similar decrease in male mating success (Joron & Brakefield 2003). In the case of the chalk hill blue butterfly ( Polyommatus coridon gennargenti ) of Sardinia, Italy, environmental heterogeneity caused landscape level habitat fragmentation, which restricted movement of butterflies between patches of habitat, thus resultin g in inbreeding (Casula et al. 2004). Saccheri et al. (1998) studied local extinction in a large metapopulation of the Glanville fritillary butterfly ( Melitaea cinxia ), and they found that decreased heterozygosity, an indication of inbreeding, significantl Some morphological characteristics change predictably with inbreeding in butterfly populations and may therefore be indicators of overall fitness. Asymmetry generally increases with inbreeding and is of ten used as a predictor of fitness level. Biologists theorize that asymmetry results from developmental accidents and thus indicates developmental instability, which in turn indicates low fitness (Clarke 1995). Inbreeding has also been shown to cause decre ased body size in butterflies (Perkins 2008, Goldish 2009), though theories for possible mechanisms behind this change have yet to be developed. In some insect species there is a strong positive correlation between body size and fecundity (Leather 1988, Ho nek 1993, Tammaru et al. 1996, Bauerfeind 2007). If body size constrains fecundity, then reduced body size as a result of inbreeding of extinction. I examined differen ces in body size and symmetry between wild caught Morpho peleides individuals and those from a population bred in captivity to observe the effects of inbreeding on morphological characteristics. Then I ran correlations between various body size measurement s and fecundity to extrapolate the effects of inbreeding on fecundity. I expected the inbred population, the one bred in captivity, to have lower overall body size, greater asymmetry, and lower fecundity. MATERIALS AND METHODS I purchased 102 Morpho pele ides pupae from a local supplier in Monteverde, Costa Rica to serve as an artificially created inbred population. All butterflies were housed in cages in the lower lab of the Biological Station in Monteverde until removed for study. I divided the pupae bet ween two small cages (1 m x 1 m x 1 m) made of PVC pipe and mosquito netting. Each pupa was pinned to a styrofoam wall within the cage, and a 60 watt light was provided for warmth. Within 24 hours of emergence, I transferred each individual to a large cage (1 m x 1 m x 2 m) made of the same materials that also contained a 60 watt light, where the young butterfly would remain for one to four days. No source of food was available to butterflies during this period. I determined the sex of each butterfly as I removed it from the large cage for study and placed it in a wax paper envelope. I terminated each butterfly by placing it in a
freezer for an hour and subsequently allowing any excess moisture to evaporate in a dehumidifying room for 30 minutes. At this po int, I massed each individual to the nearest thousandth. I also measured right and left forewing, hindwing, and antenna length with a caliper. Asymmetry was calculated as the absolute value of the difference between right and left measurements for each of these three parameters. Each female was dissected to determine the number of fully developed eggs within her abdomen. In some Lepidoptera, including M. peleides , egg development is already in process when the adult emerges but not yet complete (Wheeler 199 6). Only the fecundity results for three or four day old females were used in analysis, as these were the only age classes with adequate numbers of females containing fully developed eggs. I compared the raw data from my inbred population with the raw d ata for wild caught M. peleides individuals from studies by Perkins and Goldish (2008 and 2009, respectively.) Goldish captured wild individuals in Monteverde, Costa Rica near the Creativa School in Cerro Plano (~1500 m elevation) and the San Luis RÃo Bru ja de Monteverde (~1100 m elevation) in spring 2009. Capture sites were along roadsides near forest fragments. Perkins measured individuals from two collections consisting of butterflies captured in the Monteverde area in fall 2008 and from an online datab ase of wild caught butterflies. An analysis of variance (ANOVA) was used to determine if there were differences caught group, caught group, and my inbred group. T t ests were used to determine if measurements for the right forewing and antenna of eac h individual. Lastly, I used an ANOVA to determine the statistical significance of a regression between female body mass and fecundity. RESULTS Average right forewing length for females was greater than that for males in all three groups (Fig. 1; F = 141 .6969 , p < 0.0001, df = 5, 100). Inbred butterflies had lower average forewing length than both of the wild groups (Fig. 1; F = 144.9612 , p < 0.0001, df = 2, 103). The smallest individual was a male from the inbred group with a right forewing length of 5.0 4 cm, and the largest was a wild caught female with a right forewing length of 9.43 cm. Asymmetry did not differ between sexes (F = 1.89, p = 0.17, df = 1), so raw asymmetry values for all individuals were used to determine whether or not asymmetry differ data could not be used to analyze asymmetry because he only took measurements for the right side. There was no significant difference in asymmetry between the wild and inbred butterflies for any of the morphological characters measured (Fig. 2; antenna: t = 1.10, df = 75, P = 0.28; forewing: t = 1.20, df = 75, P = 0.23; hindwing: t = 1.02, df = 75, P = 0.31).
Mass and forewing length were positively correlated in the inbr ed butterflies (Fig. 3; r = .83, n = 68, p < 0.0001). Lastly, mass was positively correlated with number of eggs in females of the inbred group (Fig. 4; F=12.26, p=0.007, df=1,9). FIGURE 4. Number of eggs is positively correlated with mass of Morpho peleides females in an inbred population. FIGURE 3. Right forewing length is positively correlated with mass in an inbred Morpho peleides population. FIGURE 1. Average ( se) right forewing le ngth in Morpho peleides males and females of three different groups. Perkins wild and Goldish wild include wild caught butterflies from studies carried out by Perkins in fall 2008 and Goldish in spring 2009. Inbred includes butterflies purchased as pupae f rom a local supplier in Monteverde, Costa Rica. FIGURE 2. Average ( se ) symmetry values for three different morphological characters comp ared between wild caught and inbred Morpho peleides butterflies. Symmetry of an individual was measured as the difference in length between the right and left sides for each character.
DISCUSSION The larger wing size found in Morpho peleides females comp ared to males was expected. It is a long known characteristic of the species and is useful in identifying sex (Young 1972). The inbred group was shown to have significantly smaller average body size than either of the wild groups, and these results corrobo rate findings from previous studies (Perkins 2008, Goldish 2009). Similar trends have been observed in other animals (Swett et al. 1949, Fredrickson & Hedrick 2001 ), although the evolutionary reasons behind this change are pending discovery. Because fitnes s is known to decline in small, restricted populations due to inbreeding depression (Clarke 1995, Saccheri et al. 1998, Casula et al. 2004) body size may infer intraspecific fitness level in butterflies. Indeed, decreased wing size can impair flying abilit y, and antenna length plays an important role in flight balance as well as food and pheromone sensing (DeVries1987). The fact that asymmetry did not differ significantly between the wild and inbred groups suggests that asymmetry may not be a good indicato r of fitness in M. peleides . Natural wear and tear on wings due to environmental factors may compromise asymmetry measures for this particular morphological character. To ensure the accuracy and validity of asymmetry measures, perhaps studies seeking to de tect developmental instability in natural populations should choose morphological traits that are the least subject to environmental wear. However, it is also possible that differences in technique or methodology between studies factored into symmetry resu lts. Mass was only determined for individuals from the inbred population, and it was positively correlated with right forewing length, meaning larger butterflies have greater body mass. The positive correlation I found between mass and fecundity would thu s confer higher fecundity in the two wild groups. This finding may have serious consequences for establishment of future generations in inbreeding butterfly populations. Assuming inbreeding will predictably cause reduced body size, as discussed previously, fecundity would likely decrease as a result. This could, in turn, lower reproductive output, decreasing the population size in subsequent generations and further bolstering inbreeding depression. I am describing a potentially destructive positive feedback loop. DeRose and Roff (1999) found that life history traits experience greater inbreeding depression than morphological traits, and they attributed this to life history traits being more closely related to fitness. However, in this case, it is alteration of a morphological trait that constrains an important life history trait, fecundity. ACKNOWLEDGEMENTS I thank Pablo Allen for his continuous guidance and support as I struggled with uncooperative butterflies, for his help building cages, and for his pati ence in helping me build a good theoretical basis and statistical analysis last minute. Thank you to Alan Masters for his thoughtful insights for my initial experimental design. Lastly, I thank the EstaciÃ³n BiolÃ³gica de Monteverde for allowing me to use th eir facilities.
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