Sexual dimorphism and species differences in the neurophysiology and morphology of the acoustic communication system of two neotropical hylids

We examined auditory tuning and the morphology of the anatomical structures underlying acoustic communication in female Hyla microcephala and H. ebraccata and compared our findings to data from a previous study (Wilczynski et al. 1993) in which we showed species differences in the traits that in males relate to differences in the species-typical calls. Female species differences in the best excitatory frequency (BEF) of the basilar papilla (BP) were similar to the differences seen in males, and females had a significantly lower BEF in H. ebraccata, but not H. microcephala. In both species, females had lower BP thresholds. Snout-vent length, head width, and tympanic membrane diameters were sexually dimorphic in both species and larger in females, whereas laryngeal components were sexually dimorphic and larger in males. Middle and inner ear volumes were not sexually dimorphic. Despite the significant species differences in laryngeal morphology seen in males, female larynges are not significantly different. Furthermore, the interaction of species and sex differences resulted in significantly different degrees of sex dimorphism in the species, particularly for the larynx, which is more sexually dimorphic in H. microcephala, and measures of body size, which are more dimorphic in H. ebraccata. Accepted: 6 December 1996     

Features of the formation of self-fertile euploid lines (2n = 42) by self-pollination of the 46-chromosome barley-wheat BC1 hybrid Hordeum marinum subsp. gussoneanum Hudson (= H. geniculatum All.) (2n = 28) × Triticum aestivum L. (2n = 42)

We studied some features of the development of self-fertile 42-chromosome lines on the base of self-pollination progeny of 46-chromosome plants obtained by backcrossing of barley-wheat hybrids Hordeum marinum subsp. gussoneanum Hudson (= H. geniculatum All.) (2n = 28) × Triticum aestivum L. (2n = 42). The stabilization of karyotypes, resulting in 42-chromosome plants of the wheat type was generally completed by generation BC₁F₁₀. The plants of all self-pollination progenies, including BC₁F₁₀, showed some phenotypic traits characteristic of wild barley. Plants of BC₁F₁₀ with the chromosome sets 2n = 42 and 2n = 42 + t were analyzed by RAPD with a set of 115 primers. Fragments of the wild barley genome were detected in RAPD patterns with 19 primers. Cross-hybridization confirmed that these fragments belonged to the wild barley genome. We raised four phenotypically different 42-chromosome lines from grains obtained from plants of generation BC₁F₁₀, and these lines proved to be cytogenetically stable and self-fertile when grown in the field.     

Phylogenetic relationships between Afrotropical and Palaearctic Crocidura species inferred from Inter-SINE-PCR

The relationships between Afrotropical and Palaearctic Crocidurinae species have been evaluated on the basis of inter-SINE-PCR (IS-PCR). Two SINE families have been studied: mammalian interspersed repeats (MIR) and a short retroposon SOR, specific to the family Soricidae. Use of neighbor-joining and maximum parsimony analyses allowed us to recognize three major groupings: (i) 50-chromosome African species (C. parvipes and C. olivieri) and 28-chromosome European C. leucodon; (ii) species endemic to Ethiopia (36-chromosome C. thalia, C. glassi, Crocidura sp. B, united with C. macmillani and C. baileyi); (iii) Palaearctic 40-chromosome species group. Therefore, the major groupings of Crocidura shrews in the phylogenetic analysis of IS-PCR results cannot be distinguished as Palaearctic and Afrotropical groups of species: European C. leucodon unites with African 50-chromosome species with a high bootstrap support. The affiliation of Suncus murinus with Eurasian grouping is only supported by low bootstrap values.     

Experimental Population Genetics of Meiotic Drive Systems. III. Neutralization of Sex-Ratio Distortion in Drosophila through Sex-Chromosome Aneuploidy

Laboratory populations of Drosophila melanogaster were challenged by pseudo-Y drive, which mimics true Y-chromosome meiotic drive through the incorporation of Segregation Distorter (SD) in a T(Y;2) complex. This causes extreme sex-ratio distrotion and can ultimately lead to population extinction. Populations normally respond by the gradual accumulation of drive suppressors, and this reduction in strength of distortion allows the sex ratio to move closer to the optimal value of 1:1. One population monitored, however, was rapidly able to neutralize the effects of sex-ratio distortion by the accumulation of sex-chromosome aneuploids (XXY, XYY). This apparently occurs because XX-bearing eggs, produced in relatively high numbers (~4%) by XXY genotypes, become the main population source of females under strong Y-chromosome drive. Computer simulation for a discrete generation model incorporating random mating with differences in fitness and segregation permits several predictions that can be compared to the data. First, sex-chromosome aneuploids should rapidly attain equilibrium, while stabilizing the population at ~60% males. This sex ratio should be roughly independent of the strength of the meiotic drive. Moreover, conditions favoring the accumulation of drive suppressors (e.g., weak distortion, slow population extinction) are insufficient for maintaining aneuploidy, while conditions favoring aneuploidy (e.g., strong distortion, low production of females) lead to population extinction before drive suppressors can accumulate. Thus, the different mechanisms for neutralizing sex-ratio distortion are complementary. In addition, Y drive and sex-chromosome aneuploidy are potentially co-adaptive, since under some conditions neither will survive alone. Finally, these results suggest the possibility that genetic variants promoting sex-chromosome nondisjunction may have a selective advantage in natural populations faced with sex-ratio distortion.     

Chytridiomycosis impacts predator-prey interactions in larval amphibian communities

Despite ecologists increasingly recognizing pathogens as playing significant roles in community dynamics, few experimental studies have quantified patterns of disease impacts on natural systems. Amphibians are experiencing population declines, and a fungal pathogen (Batrachochytrium dendrobatidis; Chytridiomycota) is a suspected causal agent in many declines. We studied the effects of a pathogenic fungus on community interactions between the gray treefrog, Hyla chrysoscelis, and eastern newts, Notophthalmus viridescens. Recent studies have characterized chytridiomycosis as an emerging infectious disease, whose suspected rapid range expansion and widespread occurrence pose a significant risk for amphibian populations worldwide. We reared larvae in outdoor polyethylene experimental tanks and tested the effects of initial larval density, predator presence, and fungal exposure on Hyla recruitment and predator-prey interactions between Hyla and Notophthalmus. Newts reduced treefrog survival, and high intraspecific density decreased metamorphic body mass independent of B. dendrobatidis. The presence of fungi reduced treefrog body mass at metamorphosis by 34%, but had no significant main effect on survival or larval period length. B. dendrobatidis differentially affected larval development in the presence of predators; Hyla developed slower when reared with the pathogen, but only when newts were present. This significant predator-by-pathogen interaction suggests that the impact of chytridiomycosis on larval amphibians may be exacerbated in complex communities. Our data suggest that B. dendrobatidis effects on host life history may be complex and indirect. Direct measurements of the community-level effects of pathogens offer an important opportunity to understand a significant threat to global biodiversity—declining amphibian populations.     

Fine Mapping of Dominant X-Linked Incompatibility Alleles in Drosophila Hybrids

Sex chromosomes have a large effect on reproductive isolation and play an important role in hybrid inviability. In Drosophila hybrids, X-linked genes have pronounced deleterious effects on fitness in male hybrids, which have only one X chromosome. Several studies have succeeded at locating and identifying recessive X-linked alleles involved in hybrid inviability. Nonetheless, the density of dominant X-linked alleles involved in interspecific hybrid viability remains largely unknown. In this report, we study the effects of a panel of small fragments of the D. melanogaster X-chromosome carried on the D. melanogaster Y-chromosome in three kinds of hybrid males: D. melanogaster/D. santomea, D. melanogaster/D. simulans and D. melanogaster/D. mauritiana. D. santomea and D. melanogaster diverged over 10 million years ago, while D. simulans (and D. mauritiana) diverged from D. melanogaster over 3 million years ago. We find that the X-chromosome from D. melanogaster carries dominant alleles that are lethal in mel/san, mel/sim, and mel/mau hybrids, and more of these alleles are revealed in the most divergent cross. We then compare these effects on hybrid viability with two D. melanogaster intraspecific crosses. Unlike the interspecific crosses, we found no X-linked alleles that cause lethality in intraspecific crosses. Our results reveal the existence of dominant alleles on the X-chromosome of D. melanogaster which cause lethality in three different interspecific hybrids. These alleles only cause inviability in hybrid males, yet have little effect in hybrid females. This suggests that X-linked elements that cause hybrid inviability in males might not do so in hybrid females due to differing sex chromosome interactions.     

Experimental Population Genetics of Meiotic Drive Systems I. Pseudo-Y Chromosomal Drive as a Means of Eliminating Cage Populations of DROSOPHILA MELANOGASTER

The experimental population genetics of Y-chromosome drive in Drosophila melanogaster is approximated by studying the behavior of T(Y;2),SD lines. These exhibit "pseudo-Y" drive through the effective coupling of the Y chromosome to the second chromosome meiotic drive locus, Segregation distorter (SD). T(Y;2),SD males consequently produce only male offspring. When such lines are allowed to compete against structurally normal SD⁺ flies in population cages, T(Y;2),SD males increase in frequency according to the dynamics of a simple haploid selection model until the cage population is eliminated as a result of a deficiency in the number of adult females. Cage population extinction generally occurs within about seven generations.—Several conclusions can be drawn from these competition cage studies:

(1) Fitness estimates for the T(Y;2),SD lines (relative to SD⁺ ) are generally in the range of 2–4, and these values are corroborated by independent estimates derived from studies of migration-selection equilibrium.

(2) Fitness estimates are unaffected by cage replication, sample time, or the starting frequency of T(Y;2),SD males, indicating that data from diverse cages can be legitimately pooled to give an overall fitness estimate.

(3) Partitioning of the T(Y;2),SD fitnesses into components of viability, fertility, and frequency of alternate segregation (Y + SD from X + SD⁺) suggests that most of the T(Y;2),SD advantage derives from the latter two components. Improvements in the system might involve increasing both the viability and the alternate segregation to increase the total fitness.

While pseudo-Y drive operates quite effectively against laboratory stocks, it is less successful in eliminating wild-type populations which are already segregating for suppressors of SD action. This observation suggests that further studies into the origin and rate of accumulation of suppressors of meiotic drive are needed before an overall assessment can be made of the potential of Y-chromosome drive as a tool for population control.

     

Acoustic,auditory, and morphological divergence in three species of neotropical frog

Advertisement calls, auditory tuning, and larynx and ear morphology were examined in 3 neotropical frogs, Hyla microcephala, H. phlebodes and H. ebraccata, H. microcephala has the highest call dominant frequency (6.068 kHz) and basilar papilla tuning (5.36 kHz). H. phlebodes and H. ebraccata calls have lower dominant frequencies (3.832 and 3.197 kHz respectively) and basilar papilla tuning (2.79 and 2.56 kHz). The primary call notes of H. ebraccata are longer (181.6 ms) than those of H. microcephala (95.5 ms) or H. phlebodes (87.3 ms). Morphometric analysis suggests that temporal call features differ as laryngeal musculature changes, in the process changing the overall size of the larynx. The spectral aspects of the call differ as head size, and hence the size of its resonating and radiating structures, changes, modifying the dominant frequency of calls by accentuating their higher harmonics when head size decreases. Decreasing head size decreases the size of the middle and inner ear chambers, changing the mechanical tuning of the ear in the same direction as the change in dominant frequency. These changes result in divergent spectral-temporal characteristics of both the sending and receiving portions of the acoustic communication system underlying social behavior in these frogs.Abbreviations AP amphibian papilla - BEF best excitatory frequency - BP basilar papilla - dB SPL decibels sound pressure level re:20 N/m²     

When Sex Chromosomes Recombine Only in the Heterogametic Sex: Heterochiasmy and Heterogamety in Hyla Tree Frogs

Sex chromosomes are classically predicted to stop recombining in the heterogametic sex, thereby enforcing linkage between sex-determining (SD) and sex-antagonistic (SA) genes. With the same rationale, a pre-existing sex asymmetry in recombination is expected to affect the evolution of heterogamety, for example, a low rate of male recombination might favor transitions to XY systems, by generating immediate linkage between SD and SA genes. Furthermore, the accumulation of deleterious mutations on nonrecombining Y chromosomes should favor XY-to-XY transitions (which discard the decayed Y), but disfavor XY-to-ZW transitions (which fix the decayed Y as an autosome). Like many anuran amphibians, Hyla tree frogs have been shown to display drastic heterochiasmy (males only recombine at chromosome tips) and are typically XY, which seems to fit the above expectations. Instead, here we demonstrate that two species, H. sarda and H. savignyi, share a common ZW system since at least 11 Ma. Surprisingly, the typical pattern of restricted male recombination has been maintained since then, despite female heterogamety. Hence, sex chromosomes recombine freely in ZW females, not in ZZ males. This suggests that heterochiasmy does not constrain heterogamety (and vice versa), and that the role of SA genes in the evolution of sex chromosomes might have been overemphasized.     

Spatial hearing in Cope’s gray treefrog: I. Open and closed loop experiments on sound localization in the presence and absence of noise

The ability to reliably locate sound sources is critical to anurans, which navigate acoustically complex breeding choruses when choosing mates. Yet, the factors influencing sound localization performance in frogs remain largely unexplored. We applied two complementary methodologies, open and closed loop playback trials, to identify influences on localization abilities in Cope’s gray treefrog, Hyla chrysoscelis. We examined localization acuity and phonotaxis behavior of females in response to advertisement calls presented from 12 azimuthal angles, at two signal levels, in the presence and absence of noise, and at two noise levels. Orientation responses were consistent with precise localization of sound sources, rather than binary discrimination between sources on either side of the body (lateralization). Frogs were unable to discriminate between sounds arriving from forward and rearward directions, and accurate localization was limited to forward sound presentation angles. Within this region, sound presentation angle had little effect on localization acuity. The presence of noise and low signal-to-noise ratios also did not strongly impair localization ability in open loop trials, but females exhibited reduced phonotaxis performance consistent with impaired localization during closed loop trials. We discuss these results in light of previous work on spatial hearing in anurans.     

The late replication banding patterns of chromosomes are highly conserved in the genera Rana,Hyla, and Bufo (Amphibia: Anura)

Late replication banding and C-banding analyses were performed on the metaphase chromosomes of six species and one subspecies of Palearctic water frogs, genus Rana. Although C-banding patterns showed interspecific or intersubspecific variation, late replication banding patterns of all 13 chromosome pairs of these species were homologous. Minor differences of banding patterns were observed only in chromosomes 2, 7 and 13. Close comparison of the late replication banding patterns with those of three non-water frog species of Rana, and one each of Hyla and Bufo, provided important information on interspecific and intergeneric variability. In the Rana species, the banding patterns of all 13 pairs were homologous except for those some regions of 8 pairs. In one species each of Hyla and Bufo that was examined, the six large chromosome pairs (Nos. 1-6) showed banding homologies. Furthermore, among the Rana, Hyla and Bufo species the four large chromosome pairs (Nos. 1-3, 5 of Rana and Hyla, and Nos. 1, 3–5 of Bufo) shared banding homologies. These results show that the large chromosomes have been highly conserved in the evolutionary history of the three genera.     

Characterizing the host specificity of Ischnodemus variegatus (Signoret) (Hemiptera: Blissidae) on two congeneric grass species

Life history parameters of the sap-feeding bug Ischnodemus variegatus (Signoret) (Hemiptera: Blissidae) were compared between the invasive Neotropical grass, Hymenachne amplexicaulis (Rudge) Nees and the Australian native Hymenachne acutigluma (Steudel) Guilliland. Development of immatures, adult longevity, ovipositional preference and population growth of I. variegatus were compared on H. amplexicaulis and H. acutigluma under choice and no-choice conditions. Third-instar nymphs developed on both hosts but individuals reared on H. acutigluma had a 40% lower survival rate to the adult stage, 40% longer developmental time, a 9% reduction in length and a 30% reduction in weight of females compared to those reared on H. amplexicaulis. The no-choice adult longevity and oviposition study indicated that individuals feeding on H. acutigluma had half the lifespan, 62% as many ovipositing females, 52% longer time to first oviposition and only 14% as many eggs per female. Under choice conditions, females laid only 37% as many eggs on H. acutigluma as on H. amplexicaulis. Population growth of I. variegatus was slower on H. acutigluma compared to H. amplexicaulis over a 60 day period resulting in negative population increase on H. acutigluma but positive increase on H. amplexicaulis. These results reflect an overall poorer performance of I. variegatus on H. acutigluma for most life stages.     

Effects of parentage on competitive ability and vulnerability to predation in Hyla chrysoscelis tadpoles

Four sibships of Hyla chrysoscelis larvae were used to examine the effects of parentage on mass at day 23 of growth and on vulnerability to predation. The H. chrysoscelis larvae were raised alone, in competition with Rana clamitans larvae, and in competition with siblings. Vulnerability to predation by adult Notophthalmus viridescens dorsalis was evaluated for Hyla that had been raised in competition with siblings. Sibships differed in body mass and vulnerability to predation. Competition with Rana or with siblings resulted in a major reduction in body mass. There were no interactions between the effects of parentage and level of competition on body mass. Vulnerability to predation by newts appeared to be determined partially by body mass and partially by parental influences on factors other than body mass. If the differences observed between factors determining body mass and vulnerability to predation reflect negative genetic correlations among these determinants, tradeoffs between selection for increased competitive ability and reduced vulnerability to predators may partially account for the existence of genetic variation for growth rate in larval Hyla.     

Review of the marsupials (Mammalia: Metatheria) from the late Paleogene (Chadronian–Arikareean: late Eocene–late Oligocene) of North America

The taxonomy of marsupials from the late Paleogene of North America (Chadronian to Arikareean North American land mammal ages: late Eocene–late Oligocene) is reviewed based on new and previously undescribed fossil material as well as reevaluation of previously described material. Two families are recognized, the Herpetotheriidae and Peradectidae. Nine species of herpetotheriids are recognized within two genera: Herpetotherium Cope, 1873a and Copedelphys Korth, 1994, including one new species, H. tabrumi. The greatest diversity of herpetotheriids was in the Chadronian (four species). By the late Arikareean, only a single species is recognized. The range of Copedelphys is extended into the early Whitneyan (previously limited to Chadronian–Orellan). Among species of Herpetotherium, the ranges of two species have been extended: H. valens (Lambe, 1908) from the Chadronian is reported from the Orellan, and H. marsupium (Troxell, 1923) from the Uintan and Duchesnean is reported from the early Chadronian. The range of H. merriami (Stock and Furlong, 1922), previously only known from the Arikareean of Oregon, is expanded geographically eastward to Montana. Within the Peradectidae only three species are recognized: Peradectes cf. californicus (Stock, 1936) and Didelphidectes pumilis Hough, 1961 from the Chadronian, and Nanodelphys hunti (Cope, 1873b) from the Orellan to early Arikareean. Specimens previously identified as an unnamed new species of Nanodelphys from the Whitneyan and Arikareean are referred here to N. hunti.     

Age structure and body size of the Chuanxi Tree Frog Hyla annectans chuanxiensis from two different elevations in Sichuan (China)

Age, body size, and growth patterns in the subtropical anuran Hyla annectans chuanxiensis from high (Dengchigou Protection Station) and low (Lingguan Town) elevations in Baoxing County of Sichuan province (China) were described using skeletochronology. Females were significantly older than males at the low-elevation site, but there was no significant difference between the sexes at the high-elevation site. Age at sexual maturity of both males and females was 2 years at the high-elevation site, whereas males matured at 1 year and females at 2 years at the low-elevation site. Males and females from the low-elevation population reached a maximum age of 3 and 4 years, respectively, whereas males and females from the high-elevation population reached a maximum age of 4 and 5 years, respectively. At both sites, females were significantly larger than males. Females and males from the high-elevation population were larger than individuals from the low-elevation population. When the effect of age was controlled, the differences in body size of the two populations were significant only for females. Von Bertalanffy growth curves indicated that the growth rates in males was greater than in females in both populations. They also showed that the growth of both sexes slowed at an earlier age in the low-elevation population than in the high-elevation population. The findings suggest that age is a major factor underlying body size patterns for both sexes, but that the elevation of the locality affects the body size of females.     

Feeding Site Selection by Frog-Biting Midges (Diptera: Corethrellidae) on Anuran Hosts

A critical challenge of obtaining a blood meal resides in selecting a feeding site at the host. We investigate the feeding sites of species of frog-biting midges (Corethrella spp) on túngara frogs, Engystomops pustulosus (Cope), and two species of treefrogs, Dendropsophus ebraccatus (Cope) and Dendropsophus microcephalus (Cope). To investigate the differences in midge feeding sites, we performed field observations, histological sections of the frogs and examined the mouthparts of the midges. Feeding sites are predicted by the vascular properties of the skin in different body areas of the frogs. According to optimal foraging theory, the midges should feed on host body areas that maximize blood intake. Contrary to optimal foraging theory predictions, however, their feeding sites correspond to body areas with high intensity host defensive behavior.     

The genomic relationship between cultivated sorghum [Sorghum bicolor (L.) Moench] and Johnsongrass [S. halepense (L.) Pers.]: a re-evaluation

Summary The genomic relationship between cultivated sorghum [Sorghum bicolar (L.) Moench, race bicolor, De Wet, 2n=20] and Johnsongrass [S. halepense (L.) Pers., 2n=40] has been a subject of extensive studies. Nevertheless, there is no general consensus concerning the ploidy level and the number of genomes present in the two species. This research tested the validity of four major genomic models that have been proposed previously for the two species by studying chromosome behaviors in the parental species, 30-chromosome hybrids [sorghum, (2n=20) x Johnsongrass, (2n=40)], 40-chromosome hybrids [sorghum, (2n=40) x Johnsongrass, (2n=40)] and 60-chromosome amphiploids. Chromosome pairings of amphiploids are reported for the first time. Chromosomes of cultivated sorghums paired exclusively as 10 bivalents, whereas Johnsongrass had a maximum configuration of 5 ring quadrivalents with occasional hexavalents and octovalents. In contrast, 40-chromosome cultivated sorghum had up to 9 ring quadrivalents and 1 hexavalent. Pairing in the 30-chromosome hybrids showed a maximum of 10 trivalents, and that in the 40-chromosome hybrids exhibited 8 quadrivalents, 5 of which were rings, together with a few hexavalents. Amphiploid plants showed up to 3 ring hexavalents, 1 chain hexavalent and a chain of 12 chromosomes. The data suggest that cultivated sorghum is a tetraploid species with the genomic formula AAB1B1, and Johnsongrass is a segmental auto-allo-octoploid, AAAA B1B1B2B2. The model is further substantiated by chromosome pairing in amphiploid plants whose proposed genomic formula is AAAAAA B1B1B1B1 B2B2.Contribution no. 87-391-J from the Kansas Agriculatural Experiment Station     

Patterns of reproduction and habitat use in an assemblage of Neotropical hylid frogs

We censused pond-breeding hylid frogs in northeastern Costa Rica weekly for 15 months to deseribe patterns of reproduction, habitat use, and to establish baseline data on relative abundance for members of the assemblage. Reproduction in the Costa Rican assemblage was seasonal and occurred only during wet months. Some species called, but none reproduced, during the dry season. Three species (Agalychnis callidryas, Hyla ebraccata, and Scinax elaeochroa) accounted for more than 75% of the observations made during the study. The species overlapped broadly in time and space, but differed in substrate use and phenology. Two species of leaf-breeding frogs (A. callidryas and A. saltator) used perches that were significantly higher than those used by the other species. Some phenological differences were associated with different mating strategies. Explosive breeders (Scinax elaeochroa and Smilisca baudinii) were most common early in the wet seasons. Prolonged breeders (A. callidryas and H. ebraccata) were the most persistent members of this assemblage. Predation affects early and late life history stages of these hylids. Predation on arboreal egg masses by two snake species was observed. Ctenid spiders preyed on recently metamorphosed frogs and small adults. Our weekly samples were pooled into 21-day periods so that we could compare our results with those obtained for two communities of breeding anurans from South America. The patterns observed in the Costa Rican assemblage differed from those reported for South American pond-breeding frogs, but in all three assemblages reproduction was associated with wet periods.     

The Genetic Identification of a Heterochromatic Segment on the X Chromosome of DROSOPHILA MELANOGASTER

An autosomal euchromatic maternal-effect mutant, abo (= abnormal oocyte), interacts with, or regulates the activity of, the heterochromatin of the sex chromosomes of Drosophila melanogaster. It is shown that this interaction or regulation with the X chromosome involves a specific heterochromatic locus or small region that maps to the distal penultimate one-eighth of the basal X-chromosome heterochromatic segment.