PERFORMANCE OF TADPOLES FROM THE HYBRIDOGENETIC RANA ESCULENTA COMPLEX: INTERACTIONS WITH POND DRYING AND INTERSPECIFIC COMPETITION

Abstract

Abstract.»-The performance of three genotypes (LL, LR, RR) oftadpoles resulting from the hybrid mating system of Rana lessonae (phenotype L, genotype LL) and Rana esculenta (phenotype E, genotype LR) was determined in artificial ponds. The effects of interspecific competition and pond drying on growth, development, and survival of tadpoles were used to measure the performance of genotypes and the relative fitness of offspring. Among the three genotypes, tadpoles from the homogametic mating RR had the lowest survival, growth, and development under all environmental conditions. Body size of the LL and LR genotype tadpoles at metamorphosis was reduced by competition and pond drying. Days to metamorphosis were also higher for the LL and LR genotype tadpoles in competition ponds. The proportion of individuals metamorphosing of each genotype was differentially lowered by competition and pond drying. The LL genotype produced more metamorphs than the LR genotype in the constant water level ponds, but the LR genotype produced more in drying ponds. In competition ponds, the LR genotype produced more metamorphs than the LL genotype, but the LL genotype produced more metamorphs in ponds without competition. The RR genotype produced no metamorphs in any ofthe experimental environments. Increased performance of LR offspring from the heterogametic mating, in harsh conditions, and reduced performance of RR offspring from the homogametic mating, even under favorable conditions, relative to the parental genotype (LL) suggests that the population dynamics of this hybridogenetic system is strongly dependent on mate choice in mixed populations and the subsequent pond environment females select for oviposition and larval development.

Survival in adults of the water frogRana lessonaeand its hybridogenetic associateRana esculenta

“…Besides nonrandom mating (Abt and Reyer 1993;Bergen et al 1997;Roesli and Reyer 2000;Som et al 2000;Engeler and Reyer 2001), differential survival after metamorphosis could, to a certain extent, counterbalance the hybrid's initial advantage and allow R. lessonae to catch up with it in numbers. However, in contrast to the numerous studies on larval development and survivorship to metamorphosis (e.g., Wilbur 1980;Smith 1983;Riis 1991;Semlitsch and Reyer 1992a;Rowe and Dunson 1995), relatively little is known about dynamics after metamorphosis (Sjögren 1988(Sjögren , 1991Berven 1990;Neveu 1991). Since water frogs are reported to live to 6 or even 12 years of age, depending on the region they come from (Günther 1990;Sjögren 1991), the influence of adult survival is not to be neglected, and information on mortality is needed to understand population processes in these species.…”

“…In populations without R. ridibunda, the two interspecific matings (LL × LR and LR × LL) result in R. esculenta, whereas the two intraspecific matings result in either R. lessonae (LL × LL) or nonviable R. ridibunda tadpoles (RR × RR). This, plus the fact that R. esculenta is superior to R. lessonae in terms of female fecundity (Berger 1977;Berger and Uzzel 1980) and tadpole survival (Heusser and Blankenhorn 1973;Semlitsch and Reyer 1992a;Semlitsch 1993), gives the hybrid a competitive advantage over the parent species. Yet the composition of natural water frog populations in terms of species frequencies among adults seems to be quite stable over time (Berger 1983).…”

Microevolution and maternal effects on tadpole Rana temporaria growth and development rate

“…A possible scenario follows. For some frog species it has been shown or suggested that tadpoles reduce activity in the presence of predators (Skelly & Werner, 1990;Semlitsch & Reyer, 1992;Anholt & Werner, 1999), thus reducing growth rate (Skelly, 1992;Laurila & Kujasalo, 1999). It is possible that low activity level is a ®xed trait for tadpoles from some ponds (and thus persisted when raised in tanks).…”

Variation in fertilisation abilities between hemiclonal hybrid and sexual parental males of sympatric water frogs ( Rana lessonae , R. esculenta , R. ridibunda )

“…This numerical superiority of the hybrid, plus the fact that R. esculenta females produce larger clutches than R. lessonae (Berger and Uzzell 1980;Reyer et al 1999), and R. esculenta larvae perform better than R. lessonae under most ecological conditions (Semlitsch and Reyer 1992;Semlitsch 1993 gives the hybrid a reproductive advantage. If mating were random, this would initially increase the hybrid's relative abundance in mixed populations, but in the long run it would dilute the parental species out of the population and, in the absence of the necessary sexual host, lead the hybrid to extinction, too.…”

“…Homotypic LR pairings produce RR tadpoles, but these usually die during the larval stage or shortly after metamorphosis, probably because of homozygosity of deleterious mutations that have accumulated on the clonally transmitted R genome (Berger 1977;Graf and Müller 1979;Semlitsch and Reyer 1992;Vorburger 2001;Guex et al 2002).…”