Josh Van Buskirk (1959–2021)

For those of us who knew about his two-year struggle against cancer, the news should not have come as a total surprise; yet the message that Josh Van Buskirk (Fig. 1) had succumbed to the disease has deeply shaken us. We had never given up the hope that Josh would recover. We refused to believe that this friendly, enthusiastic, energetic, and brilliant man would have to go at the age of 61 and leave behind his family, many friends, and colleagues. We were particularly thinking how unfair and painful his untimely passing would be for his wife, two sons, his mother, and two sisters. But our wishful thinking was in vain. On August 20, Josh lost his battle. One thing, however, has not gone with him: the memory of what he meant to many of us. The following text with photos and the subsequent quotes from friends and colleagues may help in keeping this memory alive

Variation in Sex Ratio and Evolutionary Rate of Hemiclonal Rana esculenta Populations

In many plant and animal taxa mutation rates are higher in males than in females. As a result, the evolutionary speed of genes depends on how much time they spend in either sex. Usually, this time differs between genes located on sex chromosomes but not between those on autosomes. Here we present an unusual system with a partially sex-linked inheritance of autosomes: the hemiclonal frog Rana esculenta (E) which is originally a hybrid between the sexual species R. lessonae (L) and R. ridibunda (R). Rana esculenta excludes the L genome prior to meiosis, produces eggs or sperm containing an unrecombined R genome and restores hybridity by mating with R. lessonae (‘hybridogenesis'). Matings between L males and E females result in offspring with an even sex ratio, whereas the reverse combination produces only daughters. The extent of the resulting female bias and the proportion that R alleles have spent in either sex depend on the relative survival (b) and the relative reproductive contribution (a) of E males vs. E females. In this paper, we analyze mathematically how different combinations of a and b influence the sex ratio in R. esculenta populations and, combined with the male/female mutation rate ratio (α), the evolutionary rate of the clonally transmitted R genome. We find that this rate is higher than in an asexual population and lower than in a sexual one. Hence, clonal diversity through new mutations is more easily achievable than in purely asexual species. In contrast, the occurrence and accumulation of deleterious mutations is lower than in a comparable sexual species. We conclude that these intermediate mutation rates improve the ecological and evolutionary potential of hemiclonal organisms, and we draw attention to the implications for the use of microsatellite

Thermal and energetic consequences of nest location and breeding times in Water Pipits ( Anthus spinoletta )

Summary: The thermal environment has pronounced effects on the energy costs of thermoregulation and affects an animal's allocation of energy to self-maintenance and parental care. Consequently, the selection of reproductive periods, breeding habitats and nest-sites with a favourable microclimate can be advantageous, especially for birds breeding in harsh environments. In this study on Alpine Water Pipits (Anthus spinoletta), we evaluate the importance of spatial and temporal factors on thermoregulatory costs by combining laboratory measurements of metabolic rates under various temperatures with standard operative temperatures (Tes) recorded in the field in different microhabitats. Using these measurements we estimate the thermal and energetic consequences of nest locality and timing of reproduction. Our results show: (1) In the morning, Tes values were much higher on the east-north-east (ENE) slope of a valley than on the west-south-west (WSW) slope; in the afternoon this pattern was reversed. As a consequence, energy costs (Ehour) for thermoregulation on the ENE slope were up to 0.6 RMR (resting metabolic rate at night) lower than on the WSW slope during morning hours and about 0.8 RMR higher during afternoon hours. (2) During the incubation and nestling phases of first and second broods, total energy expenditure for thermoregulation in the daytime (Edaytime) was 0.2-0.3 RMR higher on the ENE slope than on the WSW slope. (3) Within slopes, Edaytime was lower during second broods than during first broods, with differences of 0.06-0.07 RMR during incubation and of 0.32 RMR during nestling care. These differences correspond to the flying costs of females incubating eggs (0.09 RMR) and rearing nestlings (0.25 RMR). We conclude that nest placement in relation to microclimate can improve the female's energy budget, both in terms of the total daily expenditure and its diurnal pattern. From thermal considerations alone, delaying breeding into mid-summer would be advantageous, but this advantage is probably outweighed by the reduced chances for second and replacement clutches and by the necessity to complete moult before migratio

Choosy females and indiscriminate males: mate choice in mixed populations of sexual and hybridogenetic water frogs (Rana lessonae, Rana esculenta)

For several decades, behavioral ecologists have studied the effects of the environment on the behavior of individuals; but only fairly recently they have started to ask the reverse question: how do the behavioral strategies of individuals affect the composition and dynamics of populations and communities? Although intuitively obvious, this feedback from individual to higher levels is difficult to demonstrate, except in systems with exceptionally fast and marked responses of the populations to the behavior of its members. Such a system exists in sperm-dependent species. In European water frogs, for instance, successful reproduction of a hybrid species (R. esculenta, genotype LR) requires mating with one of its parental species (R. lessonae, genotype LL), except in the rare cases where hybrids are triploid. The sexual host LL, however, should avoid matings with the sexual parasite LR, because the resulting LR offspring will eliminate the L genome from their germ line. In this study we investigate how this conflict is solved. Since water frog hybrids come in both sexes, rather than as females only like in other sperm-dependent systems, we performed the tests with both females and males. One individual was given a choice between two individuals of the opposite sex, one an LL and the other an LR. In both species, females showed the predicted preference for LL males, whereas males did not discriminate between LL and LR females. On the individual level, we interpret the sex difference in choosiness by the lower costs from mating with the wrong species (LR) and the higher benefits from mating with large individuals in males than in females. In "normal” species, male preference for large (i.e. more fecund) females is advantageous, but in this system such a choice can result in mating with the larger LR females. With respect to the structure and dynamics of mixed populations, we discuss that the observed female preference is consistent with the higher mating success of LL males found in nature. Hence, mate female choice is a strong candidate for a mechanism promoting coexistence of the sperm-dependent hybrid and its sexual host. This confirms predictions from previous theoretical model

Food supply modifies the trade-off between past and future reproduction in a sexual parasite-host system ( Rana esculenta, Rana lessonae )

Life history theory is concerned with the costs of survival, growth and reproduction under different ecological conditions and the allocation of resources to meet these costs. Typical approaches used to address these topics include manipulation of food resources, followed by measures of subsequent reproductive traits, and measures of the relationship between current and future reproductive investment. Rarely, however, do studies test for the interaction of past investment, present resource availability and future investment simultaneously. Here, we investigate this interaction in females of a sexual parasite-host system consisting of the hybridogenetic frog Rana esculenta (E) and one of its parental species Rana lessonae (L). We kept females from each of two groups (with or without previous reproduction) under two food treatments (low or high) and regularly recorded their growth as well as their body condition and hormone titres as measures of future reproductive condition. After keeping them in hibernation until the following spring, we exposed the females to males, recorded whether they spawned or not and related this response to their condition in the previous autumn. Past reproduction negatively affected growth during summer and condition during autumn which, in turn, reduced the following year's reproductive output. These costs of previous reproduction were less pronounced under the high than under the low food treatment and lower in R. lessonae than in R. esculenta. Increasing food supply improved reproductive condition more in L than in E females. These species differences in reproductive costs and food requirements provide a mechanistic explanation for why E females skip annual reproduction almost twice as often as L females. Since R. esculenta is a sexual parasite that depends on R. lessonae for successful reproduction, these species-specific life history patterns not only affect individual fitness but also the spatial structure and temporal dynamics of mixed LE population

Kryptozoologie oder: Wie tot sind die Saurier?

Im Jahr 1912 veröffentlichte der für seine Sherlock-Holmes-Krimis bekannte britische Schriftsteller Sir Arthur Conan Doyle den Roman «The Lost World». Darin erreicht eine englische Expedition in Südamerika einen Tafelberg, der sich aus der Landschaft des Amazonas-Urwaldes erhebt. Er erweist sich als ein prähistorisches Reservat mit uralten Saurier-, Vogel- und Säugetierarten, die auf dem isolierten Plateau dem Aussterben entkommen sind. Kurz: eine andernorts verlorengegangene Welt. Obwohl eindeutig als Fantasiegeschichte zu erkennen, hat das Buch die Frage aufgeworfen, ob manche urzeitliche Tiere bis heute irgendwo überlebt haben könnten – woraus sich in der Folgezeit eine eigene biologische Disziplin entwickelte: die Kryptozoologie. Deren Ziele, Methoden und Ergebnisse werden in diesem Beitrag kurz vorgestellt

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

In many species, males and females mate with multiple partners, which gives rise to sperm competition and multiple paternity. The experiments on water frogs presented here demonstrate that such sperm competition can affect the structure and dynamics of mixed-species communities. The hybrid frog Rana esculenta (LR) mates with one of its parental species, usually R. lessonae (LL), although in some areas R. ridibunda (RR), to regain the premeiotically eliminated parental genome ("hybridogenesis"). Mixed LL/LR-populations are stable although hybrid numbers should continuously increase at the expense of parental animals, because of differences in female fecundity and other factors. This would finally lead to the extinction of the sexual host, followed by that of the sexual parasite, unless the reproductive superiority of R. esculenta is reduced by other factors, such as lower hybrid male fertility. Eggs from LL- and LR-females were fertilised in vitro by single- and multi-male sperm suspensions of LL-, LR- and RR-males. In all experiments, the proportion of offspring sired by R. esculenta sperm was significantly lower than that sired by R. lessonae or R. ridibunda sperm. Gonad mass, sperm morphology, sperm swimming velocity, and sperm survival did not explain these differences in fertilisation success; nor did gamete recognition and compatibility. Sperm density was the only trait that paralleled fertilisation success, but it offers no explanation either, because densities were equalised for the in-vitro fertilisations. In natural LL/LR populations, the significantly smaller amount, poorer competitive ability and lower long-term survival of R. esculenta compared to R. lessonae sperm will reduce the initial reproductive superiority of hybrids and contribute to the stabilisation of mixed water-frog populations. Differences in fertilisation ability are also likely to be relevant for the structure and dynamics of several other systems with encounters between eggs and sperm from different genotypes, ecotypes, ploidy levels and/or specie

Mutation accumulation and fitness effects in hybridogenetic populations: a comparison to sexual and asexual systems

Background: Female only unisexual vertebrates that reproduce by hybridogenesis show an unusual genetic composition. They are of hybrid origin but show no recombination between the genomes of their parental species. Instead, the paternal genome is discarded from the germline prior to meiosis, and gametes (eggs only) contain solely unrecombined maternal genomes. Hence hybridogens only transmit maternally inherited mutations. Hybridity is restored each generation by backcrossing with males of the sexual parental species whose genome was eliminated. In contrast, recombining sexual species propagate an intermixed pool of mutations derived from the maternal and paternal parts of the genome. If mutation rates are lower in female gametes than males, it raises the possibility for lower mutation accumulation in a hybridogenetic population, and consequently, higher population fitness than its sexual counterpart. Results: We show through Monte-Carlo simulations that at higher male to female mutation ratios, and sufficiently large population sizes, hybridogenetic populations can carry a lower mutation load than sexual species. This effect is more pronounced with synergistic forms of epistasis. Mutations accumulate faster on the sexual part of the genome, and with the purifying effects of epistasis, it makes it more difficult for mutations to be transmitted on the clonal part of the genome. In smaller populations, the same mechanism reduces the speed of Muller\'s Ratchet and the number of fixed mutations compared to similar asexual species. Conclusion: Since mutation accumulation can be less pronounced in hybridogenetic populations, the question arises why hybridogenetic organisms are so scarce compared to sexual species. In considering this, it is likely that comparison of population fitnesses is not sufficient. Despite competition with the sexual parental species, hybrid populations are dependent on the maintenance of – and contact with – their sexual counterpart. Other problems may involve too little genetic diversity to respond to changing environments and problems in becoming hybridogenetic (e.g. disruption of meiosis and subsequent infertility or sterility). Yet, lower mutation accumulation in hybridogenetic populations opens the possibility that hybridogenetic species can develop into new sexual species once recombination is re-established and reproductive isolation from sexual ancestors has occurred