Eva Maria Griebeler

Biology of the sauropod dinosaurs: the evolution of gigantism

The herbivorous sauropod dinosaurs of the Jurassic and Cretaceous periods were the largest terrestrial animals ever, surpassing the largest herbivorous mammals by an order of magnitude in body mass. Several evolutionary lineages among Sauropoda produced giants with body masses in excess of 50 metric tonnes by conservative estimates. With body mass increase driven by the selective advantages of large body size, animal lineages will increase in body size until they reach the limit determined by the interplay of bauplan, biology, and resource availability. There is no evidence, however, that resource availability and global physicochemical parameters were different enough in the Mesozoic to have led to sauropod gigantism.

Plastic ingestion by pelagic and demersal fish from the North Sea and Baltic Sea

Plastic ingestion by marine biota has been reported for a variety of different taxa. In this study, we investigated 290 gastrointestinal tracts of demersal (cod, dab and flounder) and pelagic fish species (herring and mackerel) from the North and Baltic Sea for the occurrence of plastic ingestion. In 5.5% of all investigated fishes, plastic particles were detected, with 74% of all particles being in the microplastic (<5mm) size range. The polymer types of all found particles were analysed by means of Fourier transform infrared (FT-IR) spectroscopy. Almost 40% of the particles consisted of polyethylene (PE). In 3.4% of the demersal and 10.7% of the pelagic individuals, plastic ingestion was recorded, showing a significantly higher ingestion frequency in the pelagic feeders. The condition factor K was calculated to test differences in the fitness status between individuals with and without ingested plastic, but no direct effect was detected.

Evolution of avian clutch size along latitudinal gradients: do seasonality, nest predation or breeding season length matter?

Birds display a latitudinal gradient in clutch size with smaller clutches in the tropics and larger in the temperate region. Three factors have been proposed to affect this pattern: seasonality of resources (SR), nest predation and length of the breeding season (LBS). Here, we test the importance of these factors by modelling clutch size evolution within bird populations under different environmental settings. We use an individual‐based ecogenetic simulation model that combines principles from population ecology and life history theory. Results suggest that increasing SR from the tropics to the poles by itself or in combination with a decreasing predation rate and LBS can generate the latitudinal gradient in clutch size. Annual fecundity increases and annual adult survival rate decreases from the tropics to the poles. We further show that the annual number of breeding attempts that (together with clutch size) determines total annual egg production is an important trait to understand latitudinal patterns in these life history characteristics. Field experiments that manipulate environmental factors have to record effects not only on clutch size, but also on annual number of breeding attempts. We use our model to predict the outcome of such experiments under different environmental settings.

An individual based model for the conservation of the endangered Large Blue Butterfly, Maculinea arion (Lepidoptera: Lycaenidae)

Abstract European populations of the Large Blue Butterfly Maculinea arion have experienced severe declines during the 20th century, especially in the northern part of the species’ range. This endangered lycaenid butterfly needs two resources for development: flower buds of specific plants ( Thymus spp., Origanum vulgare ), on which young caterpillars briefly feed, and red ants of the genus Myrmica , whose nests support caterpillars during a prolonged final instar. In order to improve understanding of those mechanisms that are most influential to population dynamics of the butterfly, we developed a stochastic population model. This individual based model implements three main biological components relevant for population dynamics of the butterfly: (i) life on the initial host plant, (ii) adoption of the caterpillars by host ants, and (iii) life of the caterpillars within host ant nests. The model explicitly describes the spatial distribution and abundance of the butterfly, the foodplant and the host ant. Life-history parameters of the butterfly were derived from literature. Habitat characteristics such as area size, Thymus cover, density of host ant nests and proportion of adoption by non-host Myrmica ant species were obtained from a population of M. arion in the Swabian Jura (Baden-Wurttemberg, Germany). The model was successfully tested on results from studies of this natural population. A highly significant correlation between the number of individuals marked in the field and the number of individuals predicted by the model was found. A sensitivity analysis was used to test and assess general conservation measures for the Swabian population and the species in general. The Monte Carlo simulations clearly indicate that the density of host ant nests and the proportion of caterpillars adopted by non-host ant Myrmica is more critical for the survival of the butterfly than the density of its initial foodplants. A population inhabiting an area of 1 ha is likely to be regarded as safe for the next 50 years under the following conditions: Thymus cover should not fall below 5%, the proportion of adoption of caterpillars by host ants should be greater than 20%, and a minimum nest density of host ants greater than 500 per ha should be assured. Maintenance or re-establishment of grazing or mowing was successfully tested as a suitable conservation measure for declining M. arion populations.

Aging, Maturation and Growth of Sauropodomorph Dinosaurs as Deduced from Growth Curves Using Long Bone Histological Data: An Assessment of Methodological Constraints and Solutions

Information on aging, maturation, and growth is important for understanding life histories of organisms. In extinct dinosaurs, such information can be derived from the histological growth record preserved in the mid-shaft cortex of long bones. Here, we construct growth models to estimate ages at death, ages at sexual maturity, ages at which individuals were fully-grown, and maximum growth rates from the growth record preserved in long bones of six sauropod dinosaur individuals (one indeterminate mamenchisaurid, two Apatosaurus sp., two indeterminate diplodocids, and one Camarasaurus sp.) and one basal sauropodomorph dinosaur individual (Plateosaurus engelhardti). Using these estimates, we establish allometries between body mass and each of these traits and compare these to extant taxa. Growth models considered for each dinosaur individual were the von Bertalanffy model, the Gompertz model, and the logistic model (LGM), all of which have inherently fixed inflection points, and the Chapman-Richards model in which the point is not fixed. We use the arithmetic mean of the age at the inflection point and of the age at which 90% of asymptotic mass is reached to assess respectively the age at sexual maturity or the age at onset of reproduction, because unambiguous indicators of maturity in Sauropodomorpha are lacking. According to an AIC-based model selection process, the LGM was the best model for our sauropodomorph sample. Allometries established are consistent with literature data on other Sauropodomorpha. All Sauropodomorpha reached full size within a time span similar to scaled-up modern mammalian megaherbivores and had similar maximum growth rates to scaled-up modern megaherbivores and ratites, but growth rates of Sauropodomorpha were lower than of an average mammal. Sauropodomorph ages at death probably were lower than that of average scaled-up ratites and megaherbivores. Sauropodomorpha were older at maturation than scaled-up ratites and average mammals, but younger than scaled-up megaherbivores.

Reproductive Biology and Its Impact on Body Size: Comparative Analysis of Mammalian, Avian and Dinosaurian Reproduction

Janis and Carrano (1992) suggested that large dinosaurs might have faced a lower risk of extinction under ecological changes than similar-sized mammals because large dinosaurs had a higher potential reproductive output than similar-sized mammals (JC hypothesis). First, we tested the assumption underlying the JC hypothesis. We therefore analysed the potential reproductive output (reflected in clutch/litter size and annual offspring number) of extant terrestrial mammals and birds (as “dinosaur analogs”) and of extinct dinosaurs. With the exception of rodents, the differences in the reproductive output of similar-sized birds and mammals proposed by Janis and Carrano (1992) existed even at the level of single orders. Fossil dinosaur clutches were larger than litters of similar-sized mammals, and dinosaur clutch sizes were comparable to those of similar-sized birds. Because the extinction risk of extant species often correlates with a low reproductive output, the latter difference suggests a lower risk of population extinction in dinosaurs than in mammals. Second, we present a very simple, mathematical model that demonstrates the advantage of a high reproductive output underlying the JC hypothesis. It predicts that a species with a high reproductive output that usually faces very high juvenile mortalities will benefit more strongly in terms of population size from reduced juvenile mortalities (e.g., resulting from a stochastic reduction in population size) than a species with a low reproductive output that usually comprises low juvenile mortalities. Based on our results, we suggest that reproductive strategy could have contributed to the evolution of the exceptional gigantism seen in dinosaurs that does not exist in extant terrestrial mammals. Large dinosaurs, e.g., the sauropods, may have easily sustained populations of very large-bodied species over evolutionary time.

Reproductive functions of wild fish as bioindicators of reproductive toxicants in the aquatic environment

Background, aim, and scopeImpacts on the reproductive health of wild fish are thought to be suitable early-warning tools indicating contamination of surface waters with endocrine-disrupting compounds. Ecotoxicological assessment of these field observations depends on the availability of reliable biomarkers to enable a discrimination of natural variations of reproductive functions from anthropogenic impacts.Materials and methodsRoach and perch were caught at eight sampling sites by electrofishing twice a year in summer (July–September) and late autumn/winter (November–December) over a 2-year period. The sites are characterized by different degrees of anthropogenic impact and are situated within the greater Upper Rhine catchment. Age growths, parasitization and gonadal histology of more than 3,000 fish were examined.ResultsThe two dominant fish species in German surface waters perch (Perca fluviatilis L.) and roach (Rutilus rutilus L.) differ considerably regarding their suitability for biomonitoring. Even in pristine habitats, perch show several variants of sex differentiation in terms of (1) the time of first sexual maturation, (2) the course of seasonal gonadal recrudescence, and (3) the occurrence of heterologous germ cells (testes ova). A statistically significant elevated proportion of males were observed in fish obtained from a TBT-contaminated marina and suppression of gonadal ripening was observed in females caught in a sewage-contaminated brook. Both effects appear to be due to chemical contamination. The only “natural” alteration of sex differentiation in roach was related to parasitization with Ligula intestinalis (Eucestoda, Pseudophyllidea). Other deviations from the normal pattern of sex differentiation were (1) suppression of ovarian ripening and (2) asynchronic seasonal gonadal recrudescence. These are strong indicators of an anthropogenically induced impact on reproductive health. Feminization phenomena were not observed at either the individual or the population level.DiscussionInterpretation of field monitoring results concerning reproductive health requires large numbers of samples and detailed knowledge of the natural plasticity of sex differentiation in the species under investigation. A better understanding of the mechanisms underlying the plasticity of sex differentiation in perch is indispensable to enable perch to be used as a bioindicator.ConclusionsDeviation from the strict and probably endogenous control of sex differentiation in roach is a strong and unequivocal warning signal.Recommendations and perspectivesThe subject of fish monitoring should be addressed in the context of a broader spectrum of potential risks. Seasonal and ontogenetic integrity of gonadal development and recrudescence are potent biomarkers, provided the natural process is well documented for the species under investigation.

The influence of temperature model assumptions on the prognosis accuracy of extinction risk

Abstract For a species whose abundance is well-known to correlate on the degree of heat different temperature model assumptions may affect the prognosis accuracy of persistence. Likewise, year-to-year autocorrelations in weather fluctuations are known to decrease extinction risk. Thus, we investigated the grey bush cricket Platycleis albopunctata . For this species is known that growth and reproduction is mainly influenced by temperature. We developed a stochastic individual based model for the bush cricket. This day–degree model described the demographic growth of the species that depends on temperature. Daily temperatures were generated by five different methods: (i) temperatures were sequentially taken from a meteorological database. To analyse the influence of different levels of autocorrelation in temperature records (ii) the day-to-day correlations were reduced by randomly permuting the sequence of days within the months of successive years from the database, (iii) year-to-year correlations were reduced by randomly rearranging the sequence of the years held in the database, (iv) combined day-to-day and year-to-year correlations were reduced according to the submodel (ii) and (iii), and finally (v) temperatures were randomly generated on the basis of Gaussian normal distributions. The mean and the variance of these distributions depended on the date of the year. Distributions were derived from the above mentioned meteorological database. We estimated highly different minimum viable population sizes. These did severely depend on the chosen temperature model. Values ranged from 3000 adults to more than a million adults per generation. High amounts of autocorrelation in temperature values decreased the extinction risk of a bush cricket population. Permuting the sequence of the years in the database increased extinction risk less than reducing day-to-day correlations. A decrease in autocorrelation of temperature records can result in unrealistic phenologies of life stages. Decreasing day-to-day or year-to-year autocorrelation in temperature records resulted in an increase or a decrease of the duration of the egg development or the duration of larval development. For poikilothermic species general implications are presented that are relevant for the design of quantitative models used in conservation biology.

Allometries of maximum growth rate versus body mass at maximum growth indicate that non-avian dinosaurs had growth rates typical of fast growing ectothermic sauropsids.

We tested if growth rates of recent taxa are unequivocally separated between endotherms and ectotherms, and compared these to dinosaurian growth rates. We therefore performed linear regression analyses on the log-transformed maximum growth rate against log-transformed body mass at maximum growth for extant altricial birds, precocial birds, eutherians, marsupials, reptiles, fishes and dinosaurs. Regression models of precocial birds (and fishes) strongly differed from Case’s study (1978), which is often used to compare dinosaurian growth rates to those of extant vertebrates. For all taxonomic groups, the slope of 0.75 expected from the Metabolic Theory of Ecology was statistically supported. To compare growth rates between taxonomic groups we therefore used regressions with this fixed slope and group-specific intercepts. On average, maximum growth rates of ectotherms were about 10 (reptiles) to 20 (fishes) times (in comparison to mammals) or even 45 (reptiles) to 100 (fishes) times (in comparison to birds) lower than in endotherms. While on average all taxa were clearly separated from each other, individual growth rates overlapped between several taxa and even between endotherms and ectotherms. Dinosaurs had growth rates intermediate between similar sized/scaled-up reptiles and mammals, but a much lower rate than scaled-up birds. All dinosaurian growth rates were within the range of extant reptiles and mammals, and were lower than those of birds. Under the assumption that growth rate and metabolic rate are indeed linked, our results suggest two alternative interpretations. Compared to other sauropsids, the growth rates of studied dinosaurs clearly indicate that they had an ectothermic rather than an endothermic metabolic rate. Compared to other vertebrate growth rates, the overall high variability in growth rates of extant groups and the high overlap between individual growth rates of endothermic and ectothermic extant species make it impossible to rule out either of the two thermoregulation strategies for studied dinosaurs.

Distortion of symmetrical introgression in a hybrid zone: evidence for locus‐specific selection and uni‐directional range expansion

The fate of species integrity upon natural hybridization depends on the interaction between selection and dispersal. The relative significance of these processes may be studied in the initial phase of contact before selection and gene flow reach equilibrium. Here we study a hybrid zone of two salamander species, Lyciasalamandra antalyana and Lyciasalamandra billae, at the initial phase of hybridization. We quantify the degree and mode of introgression using nuclear and mtDNA markers. The hybrid zone can be characterized as an abrupt transition zone, the central hybrid zone being only c. 400 m, but introgressed genes were traced up to 3 km. Introgression was traced in both sexes but gene flow may be slightly male‐biased. Indirect evidence suggests that hybrid males are less viable than females. Introgression occurred at two levels: (1) locus‐specific selection led to different allelic introgression patterns independent of species, while (2) asymmetrical species‐level introgression occurred predominately from L. antalyana to L. billae due to range expansion of the former. This indicates that foreign genes can be incorporated into novel genomic environments, which in turn may contribute to the great diversity of morphological variants in Lyciasalamandra.