Frugivory and seed dispersal by chelonians: a review and synthesis

In recent years, it has become clear that frugivory and seed dispersal (FSD) by turtles and tortoises is much more common than previously thought. We here review published and unpublished records of chelonian FSD, and assess the role of chelonians as seed dispersers, from individual species to the community level. We first discuss the distribution of chelonian FSD and the characteristics of the fruit and/or seed species eaten and dispersed by chelonians. We then use the seed dispersal efficiency framework to explore the quantitative and qualitative components of seed dispersal by tortoises and turtles, embarking on a journey from when the fruits and/or seeds are consumed, to when and where they are deposited, and assess how efficient chelonians are as seed dispersers. We finally discuss chelonian FSD in the context of communities and of chelonians as megafauna. A substantial proportion of the world's aquatic and terrestrial turtles and a major part of testudinid tortoises (71 species in 12 families) include fruits and/or seeds in their diet; fruits of at least 588 plant species in 121 families are ingested and/or dispersed by chelonians. For some chelonians, overall or in certain seasons, fruit may even form the largest part of their diet. Contrary to seed dispersal by lizards, the other major reptilian frugivores, chelonian FSD is not an island phenomenon in terms of geographic distribution. Nevertheless, on islands tortoises are often among the largest native terrestrial vertebrates - or were until humans arrived. We synthesise our knowledge of chelonian FSD, and discuss the relevance of our findings for conservation and restoration, especially in relation to rewilding with large and giant tortoises.

Frugivory and seed dispersal by chelonians: a review and synthesis

In recent years, it has become clear that frugivory and seed dispersal (FSD) by turtles and tortoises is much more common than previously thought. We here review published and unpublished records of chelonian FSD, and assess the role of chelonians as seed dispersers, from individual species to the community level. We first discuss the distribution of chelonian FSD and the characteristics of the fruit and/or seed species eaten and dispersed by chelonians. We then use the seed dispersal efficiency framework to explore the quantitative and qualitative components of seed dispersal by tortoises and turtles, embarking on a journey from when the fruits and/or seeds are consumed, to when and where they are deposited, and assess how efficient chelonians are as seed dispersers. We finally discuss chelonian FSD in the context of communities and of chelonians as megafauna. A substantial proportion of the world's aquatic and terrestrial turtles and a major part of testudinid tortoises (71 species in 12 families) include fruits and/or seeds in their diet; fruits of at least 588 plant species in 121 families are ingested and/or dispersed by chelonians. For some chelonians, overall or in certain seasons, fruit may even form the largest part of their diet. Contrary to seed dispersal by lizards, the other major reptilian frugivores, chelonian FSD is not an island phenomenon in terms of geographic distribution. Nevertheless, on islands tortoises are often among the largest native terrestrial vertebrates - or were until humans arrived. We synthesise our knowledge of chelonian FSD, and discuss the relevance of our findings for conservation and restoration, especially in relation to rewilding with large and giant tortoises.

Evaluation of artificial heating sources for the thermoregulation of Aldabra giant tortoises (Aldabrachelys gigantea) in Zurich zoo

We recorded the thermoregulatory patterns of five Aldabra giant tortoises (Aldabrachelys gigantea) (25-193 kg) during spring (ZRH spring trial), after the installation of a heating area (concrete heat pad and basking lamp) at Zurich Zoo, Switzerland. The measurements were compared to published results on the same tortoises observed prior to the installation of the heater (ZRH summer and winter trials), and on wild tortoises on Aldabra Atoll. The mean environmental temperature outside the heating area was 23.3 °C, significantly lower compared to Aldabra Atoll (30.3 °C; range: 23.8-43.8 °C), and to the environmental temperature range at which tortoises maximize their activity in the wild (T_a-opt ; 25.8-31.7 °C). The heating area exhibited a mean temperature of 36.3 °C, and tortoises that made use of the heating area were able to maintain a mean core body temperature (T_bc ) of 30.0 °C, which was comparable to the T_bc of tortoises during ZRH summer and on Aldabra trials, and an improvement over the mean T_bc recorded during the ZRH winter trial (21.2 °C). The smaller individuals reached the upper limits of T_bc recommended for the species, probably due to heating pad temperatures above T_a-opt . We discuss current practices to provide external heating sources for tortoises and how this method can be used to provide an adequate thermal environment for large captive reptiles. Finally, we provide recommendations for the installation of artificial heating sources for tortoises and large reptiles.

Island rewilding with giant tortoises in an era of climate change

Replacing recently extinct endemic giant tortoises with extant, functional analogues provide the perhaps best examples of island rewilding to date. Yet, an efficient future application of this conservation action is challenging in an era of climate change. We here present and discuss a conceptual framework that can serve as a roadmap for the study and application of tortoise rewilding in an uncertain future. We focus on three main ecological functions mediated by giant tortoises, namely herbivory, seed dispersal and nutrient cycling, and discuss how climate change is likely to impact these. We then propose and discuss mitigation strategies such as artificial constructed shade sites and water holes that can help drive and maintain the ecosystem functions provided by the tortoises on a landscape scale. The application of the framework and the mitigation strategies are illustrated with examples from both wild and rewilded populations of the Aldabra giant tortoise, Aldabrachelys gigantea, in the Western Indian Ocean.This article is part of the theme issue 'Trophic rewilding: consequences for ecosystems under global change'.

Patterns of activity and body temperature of Aldabra giant tortoises in relation to environmental temperature

We studied the temperature relations of wild and zoo Aldabra giant tortoises (Aldabrachelys gigantea) focusing on (1) the relationship between environmental temperature and tortoise activity patterns (n = 8 wild individuals) and (2) on tortoise body temperature fluctuations, including how their core and external body temperatures vary in relation to different environmental temperature ranges (seasons; n = 4 wild and n = 5 zoo individuals). In addition, we surveyed the literature to review the effect of body mass on core body temperature range in relation to environmental temperature in the Testudinidae. Diurnal activity of tortoises was bimodally distributed and influenced by environmental temperature and season. The mean air temperature at which activity is maximized was 27.9°C, with a range of 25.8-31.7°C. Furthermore, air temperature explained changes in the core body temperature better than did mass, and only during the coldest trial, did tortoises with higher mass show more stable temperatures. Our results, together with the overall Testudinidae overview, suggest that, once variation in environmental temperature has been taken into account, there is little effect of mass on the temperature stability of tortoises. Moreover, the presence of thermal inertia in an individual tortoise depends on the environmental temperatures, and we found no evidence for inertial homeothermy. Finally, patterns of core and external body temperatures in comparison with environmental temperatures suggest that Aldabra giant tortoises act as mixed conformer-regulators. Our study provides a baseline to manage the thermal environment of wild and rewilded populations of an important island ecosystem engineer species in an era of climate change.

Trophic interactions between larger crocodylians and giant tortoises on Aldabra Atoll, Western Indian Ocean, during the Late Pleistocene

Today, the UNESCO World Heritage Site of Aldabra Atoll is home to about 100 000 giant tortoises, Aldabrachelys gigantea, whose fossil record goes back to the Late Pleistocene. New Late Pleistocene fossils (age ca. 90-125 000 years) from the atoll revealed some appendicular bones and numerous shell fragments of giant tortoises and cranial and postcranial elements of crocodylians. Several tortoise bones show circular holes, pits and scratch marks that are interpreted as bite marks of crocodylians. The presence of a Late Pleistocene crocodylian species, Aldabrachampsus dilophus, has been known for some time, but the recently found crocodylian remains presented herein are distinctly larger than those previously described. This indicates the presence of at least some larger crocodylians, either of the same or of a different species, on the atoll. These larger crocodylians, likely the apex predators in the Aldabra ecosystem at the time, were well capable of inflicting damage on even very large giant tortoises. We thus propose an extinct predator-prey interaction between crocodylians and giant tortoises during the Late Pleistocene, when both groups were living sympatrically on Aldabra, and we discuss scenarios for the crocodylians directly attacking the tortoises or scavenging on recently deceased animals.

Decline in abundance and health state of an Atlantic subtropical gorgonian population

Losses in coral cover have been widely reported for the Caribbean. In contrast, much less is known about the health state of the Brazilian reef fauna, which was declared as a priority for Atlantic biodiversity conservation due to its high degree of endemism. In the present study, we assessed the general health state of Phyllogorgia dilatata assemblages at the subtropical reefs of Arraial do Cabo (southeastern Brazil), where observations suggest that the abundance of this endemic gorgonian species has declined. We found that about 49% of the sampled colonies were dead, and 73% of the living colonies were affected by tissue loss. Tissue loss initially manifested as multifocal holes in the planar colonial coenenchyme and peripheral tissue retraction leaving denuded skeletal axes. In combination with other recent studies, our results raise the awareness for an increasingly threatened Southwestern Atlantic reef coral fauna.

Persistence of distinctive morphotypes in the native range of the CITES-listed Aldabra giant tortoise

Understanding the extent of morphological variation in the wild population of Aldabra giant tortoises is important for conservation, as morphological variation in captive populations has been interpreted as evidence for lingering genes from extinct tortoise lineages. If true, this could impact reintroduction programmes in the region. The population of giant tortoises on Aldabra Atoll is subdivided and distributed around several islands. Although pronounced morphological variation was recorded in the late 1960s, it was thought to be a temporary phenomenon. Early researchers also raised concerns over the future of the population, which was perceived to have exceeded its carrying capacity. We analyzed monthly monitoring data from 12 transects spanning a recent 15‐year period (1998–2012) during which animals from four subpopulations were counted, measured, and sexed. In addition, we analyzed survival data from individuals first tagged during the early 1970s. The population is stable with no sign of significant decline. Subpopulations differ in density, but these differences are mostly due to differences in the prevailing vegetation type. However, subpopulations differ greatly in both the size of animals and the degree of sexual dimorphism. Comparisons with historical data reveal that phenotypic differences among the subpopulations of tortoises on Aldabra have been apparent for the last 50 years with no sign of diminishing. We conclude that the giant tortoise population on Aldabra is subject to varying ecological selection pressures, giving rise to stable morphotypes in discrete subpopulations. We suggest therefore that (1) the presence of morphological differences among captive Aldabra tortoises does not alone provide convincing evidence of genes from other extinct species; and (2) Aldabra serves as an important example of how conservation and management in situ can add to the scientific value of populations and perhaps enable them to better adapt to future ecological pressures.

Non-native megaherbivores: the case for novel function to manage plant invasions on islands

There is a heated debate about whether all non-native species are 'guilty until proven innocent', or whether some should be accepted or even welcomed. Further fanning the flames, I here present a case where introductions of carefully vetted, non-native species could provide a net conservation benefit. On many islands, native megaherbivores (flightless birds, tortoises) recently went extinct. Here, rewilding with carefully selected non-native species as ecological replacements is increasingly considered a solution, reinstating a herbivory regime that largely benefits the native flora. Based on these efforts, I suggest that restoration practitioners working on islands without a history of native megaherbivores that are threatened by invasive plants should consider introducing a non-native island megaherbivore, and that large and giant tortoises are ideal candidates. Such tortoises would be equally useful on islands where eradication of invasive mammals has led to increased problems with invasive plants, or on islands that never had introduced mammalian herbivores, but where invasive plants are a problem. My proposal may seem radical, but the reversibility of using giant tortoises means that nothing is lost from trying, and that indeed much is to be gained. As an easily regulated adaptive management tool, it represents an innovative, hypothesis-driven 'innocent until proven guilty' approach.

Indirect and direct relations between aerobic fitness, physical activity, and academic achievement in elementary school students

BACKGROUND

There is evidence to suggest that increasing physical activity (PA) improves academic achievement (AA) in children and that aerobic fitness is associated with both cognitive function and AA. However, it is not known how these variables are interrelated and analyses with adequate control for socioeconomic variables are needed. It was hypothesized that PA would not directly affect AA but would have an indirect effect on AA through its effect on aerobic fitness. The purpose of this study was to test this hypothesized mediation using path analysis.

METHODS

Cross-sectional data including AA, aerobic fitness, and daily PA assessed through accelerometry were collected from a large sample (N = 687) of 2nd and 3rd grade students. Demographic data were assessed via parent self-report.

RESULTS

A total of 401 students wore the accelerometer for at least 10 hours on 3 days or more and were included in the final path analysis to evaluate potential relations among PA (predictor), aerobic fitness (mediator), and WIAT-III subtest standard scores (outcomes; i.e., reading, spelling, and mathematics). Findings showed a direct effect of PA on aerobic fitness (b = 0.009, p < 0.001) and an indirect effect (mediation) of PA via fitness on math achievement (b = 0.003, p < 0.01) after controlling for student's grade, gender, body mass index, mother's education level, and household income, as well as intraclass correlations among classes and schools. Neither PA nor aerobic fitness were correlated with WIAT-III reading or spelling scores.

CONCLUSIONS

Mediation analysis indicated that PA exerted an influence on math achievement through its effects on aerobic fitness but was not associated with reading or spelling achievement scores.

Floral signposts: testing the significance of visual 'nectar guides' for pollinator behaviour and plant fitness

Nectar guides, contrasting patterns on flowers that supposedly direct pollinators towards a concealed nectar reward, are taxonomically widespread. However, there have been few studies of their functional significance and effects on plant fitness. Most previous studies focused on pollinator behaviour and used artificial flowers in laboratory settings. We experimentally investigated the role of putative nectar guides in a natural system: the South African iris Lapeirousia oreogena, whose flowers have a clearly visible pattern of six white arrow-markings pointing towards the narrow entrance of the long corolla tube, and its sole pollinator, a long-proboscid nemestrinid fly. We painted over none, some or all of the white arrow-markings with ink that matched the colour of the corolla background. Although arrow-marking removal had little effect on the approaches by flies to flowers from a distance, it dramatically reduced the likelihood of proboscis insertion. Export of pollen dye analogue (an estimate of male fitness) was reduced to almost zero in flowers from which all nectar guides had been removed, and fruit set (a measure of female fitness) was also significantly reduced. Our results confirm that the markings on L. oreogena flowers serve as nectar guides and suggest that they are under strong selective maintenance through both male and female fitness components in this pollination system.

Carrion mimicry in a South African orchid: flowers attract a narrow subset of the fly assemblage on animal carcasses

BACKGROUND AND AIMS

Although pollination of plants that attract flies by resembling their carrion brood and food sites has been reported in several angiosperm families, there has been very little work done on the level of specificity in carrion mimicry systems and the importance of plant cues in mediating such specialization. Specificity may be expected, as carrion-frequenting flies often exploit different niches, which has been interpreted as avoidance of interspecific competition. Interactions between the orchid Satyrium pumilum and a local assemblage of carrion flies were investigated, and the functional significance of floral traits, especially scent, tested. Pollination success and the incidence of pollinator-mediated self-pollination were measured and these were compared with values for orchids with sexual- and food-deceptive pollination systems.

METHODS AND KEY RESULTS

Observations of insect visitation to animal carcasses and to flowers showed that the local assemblage of carrion flies was dominated by blow flies (Calliphoridae), house flies (Muscidae) and flesh flies (Sarcophagidae), but flowers of the orchid were pollinated exclusively by flesh flies, with a strong bias towards females that sometimes deposited live larvae on flowers. A trend towards similar partitioning of fly taxa was found in an experiment that tested the effect of large versus small carrion quantities on fly attraction. GC-MS analysis showed that floral scent is dominated by oligosulfides, 2-heptanone, p-cresol and indole, compounds that also dominate carrion scent. Flesh flies did not distinguish between floral and carrion scent in a choice experiment using olfactory cues only, which also showed that scent alone is responsible for fly attraction. Pollination success was relatively high (31·5 % of flowers), but tracking of stained pollinia also revealed that a relatively high percentage (46 %) of pollen deposited on stigmas originates from the same plant.

CONCLUSIONS

Satyrium pumilum selectively attracts flesh flies, probably because its relatively weak scent resembles that of the small carrion on which these flies predominate. In this way, the plants exploit a specific subset of the insect assemblage associated with carrion. Pollination rates and levels of self-pollination were high compared with those in other deceptive orchids and it is therefore unlikely that this mimicry system evolved to promote outcrossing.

Positive Indirect Interactions between Neighboring Plant Species via a Lizard Pollinator

In natural communities, species are embedded in networks of direct and indirect interactions. Most studies on indirect interactions have focused on how they affect predator-prey or competitive relationships. However, it is equally likely that indirect interactions play an important structuring role in mutualistic relationships in a natural community. We demonstrate experimentally that on a small spatial scale, dense thickets of endemic Pandanus plants have a strong positive trait-mediated indirect effect on the reproduction of the declining endemic Mauritian plant Trochetia blackburniana. This effect is mediated by the endemic gecko Phelsuma cepediana moving between Pandanus thickets, a preferred microhabitat, and nearby T. blackburniana plants, where it feeds on nectar and pollinates the plants. Our findings emphasize the importance of considering plant-animal interactions such as pollination at relatively small spatial scales in both basic ecological studies and applied conservation management.

Coloured nectar: distribution, ecology, and evolution of an enigmatic floral trait

While coloured nectar has been known to science at least since 1785, it has only recently received focused scientific attention. However, information about this rare floral trait is scattered and hard to find. Here, we document coloured nectar in 67 taxa worldwide, with a wide taxonomical and geographical distribution. We summarise what is currently known about coloured nectar in each of the lineages where it occurs. The most common nectar colours are in the spectrum from yellow to red, but also brown, black, green, and blue colours are found. Colour intensity of the nectar varies, sometimes even within one taxa, as does the level of contrast between flower petals and nectar. Coloured nectar has evolved independently throughout the angiosperms at least 15 times at the level of family, and is in many cases correlated with one or more of three parameters: (1) vertebrate pollination, known or hypothesised, (2) insularity -- many species are from islands or insular mainland habitats, and (3) altitude -- many species are found at relatively high altitudes. We discuss the evolution and speculate on possible ecological functions of coloured nectar. Apart from being a non-functional, perhaps pleiotropic, trait, we present several hypotheses on possible ecological functions of coloured nectar. Firstly, for some plant species it can be interpreted as an honest signal, leading to high pollination efficiency. Secondly, it can function as a deterrent against nectar-thieves or inefficient pollinators, thus acting as a floral filter. Thirdly, nectar colour-pigments can have anti-microbial qualities that may protect the nectar in long-lived flowers. Neither of these possibilities are mutually exclusive. Recent studies have provided experimental evidence for the first two hypotheses, and we suggest promising avenues for future research into this little-known floral trait.

Mauritian coloured nectar no longer a mystery: a visual signal for lizard pollinators

Most floral nectars are clear as water, and the enigmatic coloured nectar in three endemic plant species in Mauritius has puzzled scientists studying it. One hypothesis about the possible ecological function of coloured nectar is that it serves as a visual signal for pollinators. Recent studies have shown that at least two of the three Mauritian plant species with coloured nectar are visited and pollinated by endemic Phelsuma geckos. We here provide experimental evidence for the visual signal hypothesis by showing that Phelsuma ornata geckos prefer coloured over clear nectar in artificial flowers. In flowering plants, coloured nectar could additionally function as an honest signal that allows pollinators to assert the presence and judge the size of a reward prior to flower visitation, and to adjust their behaviour accordingly, leading to increased pollinator efficiency. Our study provides a first step in understanding this rare and intriguing floral trait.

Influence of dosage regimen on responses of the arcuate nucleus to subcutaneous injection of a protein hydrolysate

The effect of administration of a glutamate-containing protein hydrolysate on the arcuate nucleus of 10-day-old mice was studied by two methods. Arcuate nucleus damage resulted when administration was by a single large subcutaneous dose (100 ml/kg). When the same total dose was administered subcutaneously in five small doses (20 ml/kg) over a period of 8 h, the damage to the arcuate nucleus did not occur. The latter method of administration was to simulate a clinical infusion. The results demonstrate that there is no hazard to the arcuate nucleus w-en glutamate-containing protein hydrolysates are administered by infusion.