ADVERTISEMENT CALLS OF THE TREE FROGS,HYLA ARBOREA AND HYLA SAVIGNYI (ANURA: HYLIDAE) IN TURKEY

ABSTRACT

The systematic classification of tree frogs (Hyla) inhabiting different regions of the country of Turkey is unclear. Recordings of natural advertisement calls of individual male tree frogs in different locations in Turkey were analyzed to determine variation in acoustic features that may be related to taxonomic status. Multivariate analysis of covariance showed that call duration, intercali interval and number of pulses per call varied significantly between frogs in different locales. Call duration, intercall interval, and number of pulses per call were related to air temperature. Dominant frequency differed significantly between different groups of frogs, and was temperature-independent. These data are consistent with the hypothesis that tree frogs in Turkey represent two distinct species, Hyla arborea and Hyla savignyi.     

PHYLOGENETIC EVIDENCE FOR COMPETITIVELY DRIVEN DIVERGENCE: BODY-SIZE EVOLUTION IN CARIBBEAN TREEFROGS (HYLIDAE: OSTEOPILUS)

Understanding the role of competition in explaining phenotypic diversity is a challenging problem, given that the most divergent species may no longer compete today. However, convergent evolution of extreme body sizes across communities may offer evidence of past competition. For example, many treefrog assemblages around the world have convergently evolved species with very large and small body sizes. To better understand this global pattern, we studied body-size diversification within the small, endemic radiation of Caribbean treefrogs ( Osteopilus ). We introduce a suite of analyses designed to help reveal the signature of past competition. Diet analyses show that Osteopilus are generalist predators and that prey size is strongly associated with body size, suggesting that body-size divergence facilitates resource partitioning. Community assembly models indicate that treefrog body-size distributions in Jamaica and Hispaniola are consistent with expectations from competition. Phylogenetic analyses show that similar body-size extremes in Jamaica and Hispaniola have originated through parallel evolution on each island, and the rate of body-size evolution in Osteopilus is accelerated relative to mainland treefrogs. Together, these results suggest that competition may have driven the rapid diversification of body sizes in Caribbean treefrogs to the extremes seen in treefrog communities around the world.     

PHYLOGENETIC ANALYSES REVEAL UNEXPECTED PATTERNS IN THE EVOLUTION OF REPRODUCTIVE MODES IN FROGS

Understanding phenotypic diversity requires not only identification of selective factors that favor origins of derived states, but also factors that favor retention of primitive states. Anurans (frogs and toads) exhibit a remarkable diversity of reproductive modes that is unique among terrestrial vertebrates. Here, we analyze the evolution of these modes, using comparative methods on a phylogeny and matched life‐history database of 720 species, including most families and modes. As expected, modes with terrestrial eggs and aquatic larvae often precede direct development (terrestrial egg, no tadpole stage), but surprisingly, direct development evolves directly from aquatic breeding nearly as often. Modes with primitive exotrophic larvae (feeding outside the egg) frequently give rise to direct developers, whereas those with nonfeeding larvae (endotrophic) do not. Similarly, modes with eggs and larvae placed in locations protected from aquatic predators evolve frequently but rarely give rise to direct developers. Thus, frogs frequently bypass many seemingly intermediate stages in the evolution of direct development. We also find significant associations between terrestrial reproduction and reduced clutch size, larger egg size, reduced adult size, parental care, and occurrence in wetter and warmer regions. These associations may help explain the widespread retention of aquatic eggs and larvae, and the overall diversity of anuran reproductive modes.     

THE EFFECTS OF THE MATING SYSTEM ON PROGENY PERFORMANCE IN HYLA CRUCIFER (ANURA: HYLIDAE)

We performed a controlled mating experiment to determine whether genetic variation in larval traits in Hyla crucifer was predictable on the basis of mating status or body size of male parent. Larval growth rate was predictably related to body size of the sire. Males from the upper half of the body-size distribution sired offspring with 6% higher growth rates than those of offspring sired by males from the lower half of the body-size distribution. Offspring sired by males that obtained mates in nature had 3% higher growth rates than their half-siblings sired by males that did not mate in nature. Genetic variation for larval-period duration and size at metamorphosis was detected; however, neither mating status nor body size of sire could be used to predict values of these traits in the progeny. Although all three larval traits can affect fitness, there was no evidence that the offspring of some sires would always outperform the offspring of others in all three traits. The predictable association between adult male size and larval growth rate means that the H. crucifer mating system would have a directional effect on larval growth rate if male body size influences the outcome of male-male competition or female choice.     

VARIATION IN THE CODING OF SPECIES IDENTITY IN THE ADVERTISEMENT CALLS OF LITORIA VERREAUXI (ANURA: HYLIDAE)

Variation within and among males was documented in two properties of the advertisement call of Litoria verreauxi; comparisons were also made between populations of L. verreauxi that were allopatric and sympatric with L. ewingi. Pulse rate, a property of known importance in mate recognition, was stereotyped. However, a character upon which the full expression of pulse rate depends, the depth of amplitude modulation (AM) or pulsing, was significantly lower and more variable in populations of L. verreauxi that coexisted with L. ewingi than in allopatric populations of L. verreauxi. Furthermore, there were significant changes in the depth of AM in the calls of sympatric males recorded from one night to another within the breeding season. The within-male variation (between recordings) in this character within sympatric populations was so great that statistically significant differences between males could not be detected. Thus, even if gravid females in sympatry choose a male on the basis of the degree to which his calls are pulsed, the evolutionary response to such selection would probably be very limited. The change that appears to be occurring in the temporal code for species identity vis-à-vis L. ewingi in sympatry (a change from a quantitative difference [pulse rate] to a qualitative one [pulsed versus unpulsed calls]) is probably a passive consequence of the shift to higher pulse rates.     

EVOLUTIONARY TRENDS IN FROGS

Fossil evidence concerning the Anura adds guide-lines to phylogeneticinterpretations, but in large part evolutionary informationhas come from comparative studies of moderns. Trends withinthe Anura, established in different lines, provide an importantsource of clues for major phylogenetic interpretations. A numberof such trends, both osteological and non-skeletal, are analyzedand their phylogenetic implications assessed. Two major lines of development are postulated. One branch includesthe notobatrachid-ascaphid and the pipid-rhinophynid sublines.The other major branch includes the advanced frogs with procoelouscentra. The advanced frogs were derived from a primitive stockprior to the development of anything that would be recognizedas a notobatrachid-ascaphid-opisthocoelan line, rather thanfrom such a line.     

HYBRIDIZATION IN LEOPARD FROGS (RANA PIPIENS COMPLEX): LARVAL FITNESS COMPONENTS IN SINGLE-GENOTYPE POPULATIONS AND MIXTURES

Recognizing the predominant mode of selection in hybrid systems is important in predicting the evolutionary fate of recombinant genotypes. Natural selection is endogenous if hybrid genotypes are at a disadvantage relative to parental species independent of environment. Alternatively, relative fitness can vary in response to environmental variation (exogenous selection), and hybrid genotypes can possess fitness values equal to or greater than that of parental species. I investigated the nature of natural selection in a leopard frog hybrid system by rearing larvae of hybrid and parental genotypes between Rana blairi and R. sphenocephala in 1000-L outdoor experimental ponds. Three hybrid (F₁, backcrossj [B₁], backcross₂ [B₂]) and two parental (R. blairi [BB] and R. sphenocephala [SS]) larval genotypes were produced by artificial fertilzations using adult frogs from a natural population in central Missouri. Resultant larvae were reared in single-genotype populations and two-way mixtures at equal total numbers from hatching to metamorphosis. In single-genotype ponds, F₁ hybrid larvae had highest survival and BB were largest at metamorphosis. When F₁ and SS larvae were mixed together, F₁ hybrids had reduced survival and both F₁ and SS larvae metamorphosed at larger body masses than when reared separately. When mixed, both B₁ and SS larvae had shorter larval period lengths than when reared alone. Higher proportion of B₁ metamorphs were produced when larvae were mixed with either parental species than when reared alone. Larval fitness components as measured by survival, body mass at metamorphosis, proportion of survivors metamorphosing, and larval period length for B₂ hybrid and BB larvae were similar in single-genotype populations and mixtures. Comparison of composite fitness component estimates indicated hybrid genotypes possess equivalent or higher larval fitness relative to both parental species for the life-history fitness components measured. Despite reduced survival of F₁ hybrids in mixtures, backcross-generation hybrid genotypes demonstrated high levels of larval growth, survival, and metamorphosis in mixtures with parental species. Consequently, this study suggests natural hybridization and subsequent backcrossing between R. blairi and R. sphenocephala can produce novel and relatively fit hybrid genotypes capable of successful existence with parental species larvae. Thus, the evolutionary fate of hybrid and parental genotypes in this system may be influenced by exogenous selection mediated by genotypic composition of larval assemblages.     

LATITUDINAL VARIATION IN SPECIATION MECHANISMS IN FROGS

Speciation often has a strong geographical and environmental component, but the ecological factors that potentially underlie allopatric and parapatric speciation remain understudied. Two ecological mechanisms by which speciation may occur on geographic scales are allopatric speciation through niche conservatism and parapatric or allopatric speciation through niche divergence. A previous study on salamanders found a strong latitudinal pattern in the prevalence of these mechanisms, with niche conservatism dominating in temperate regions and niche divergence dominating in the tropics, and related this pattern to Janzen's hypothesis of greater climatic zonation between different elevations in the tropics. Here, we test for latitudinal patterns in speciation in a related but more diverse group of amphibians, the anurans. Using data from up to 79 sister-species pairs, we test for latitudinal variation in elevational and climatic overlap between sister species, and evaluate the frequency of speciation via niche conservatism versus niche divergence in relation to latitude. In contrast to salamanders, we find no tendency for greater niche divergence in the tropics or for greater niche conservatism in temperate regions. Although our results support the idea of greater climatic zonation in tropical regions, they show that this climatic pattern does not lead to straightforward relationships between speciation, latitude, and niche evolution.     

MARSUPIAL ANATOMY OF THE DEMIBRANCH OF MARGARITIFERA MARGARITIFERA (LIN.) IN NORTHEASTERN NORTH AMERICA (PELECYPODA: UNIONACEA)

On morphological, biological and behavioral characters the freshwatermussel family Margaritiferidae generally is accepted as themost primitive of the Unionacea. Microscopic examination ofthe marsupial demibranch further supports this assumption, inthat the interlamellar junctions lack elastic properties necessaryfor lateral hyperextension of the gravid demibranch. A temporarymodification of marsupial anatomy in the form of a fibrous elastinaccessory material is produced during the final phase of glochidialincubation. Its appearance coincides with the enlargement ofepithelial cells that line the marsupium and interlamellar junctions.The material, which is situated between the glochidial massand the inner lamellar surfaces, may provide increased aerationand support for the resting glochidia. (Received 18 February 1978;     

PATTERNS OF POSTZYGOTIC ISOLATION IN FROGS

From literature data on 116 taxa crosses involving 46 species of frogs, we found a positive correlation between degree of divergence (measured as Nei's genetic distance, D) and degree of postzygotic isolation. In anurans, hybrid sterility appears to evolve more quickly than inviability, which is consistent with the conclusions of other studies that involved Drosophila species. The lower threshold of D = 0.30 for evolution of hybrid inviability that we found is similar to that observed for Drosophila. This consistency suggests that there may be a general pattern in the acquisition of reproductive isolation in animals.