| 11. |
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| 12. |
- Kelehear, Crystal, et al.
(författare)
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Interactions between infective helminth larvae and their anuran host
- 2011
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Ingår i: Herpetologica. - 0018-0831 .- 1938-5099. ; 67:4, s. 378-385
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Tidskriftsartikel (refereegranskat)abstract
- Detailed observations on interactions between parasites and prospective hosts during the infection process can clarify (1) the routes by which parasites enter the host and (2) the ability of prospective hosts to detect, avoid, or resist potential parasites. Such information can clarify determinants of host vulnerability. Infective larvae of the nematode Rhabdias pseudosphaerocephala entered the bodies of their anuran host the Cane Toad (Rhinella marina, formerly Bufo marinus) primarily through the orbit (i.e., by crawling over the surface of the toad's eye) rather than by burrowing through the skin (believed to be the usual route of infection for rhabditid parasites). In our experimental infections, metamorph Cane Toads detected infective R. pseudosphaerocephala larvae but did not avoid them, nor did they manage to restrict rates of infective larvae penetration by using behavioral means (the toads kicked at infective larvae but failed to dislodge them). Rhabdias pseudosphaerocephala cause damage to their toad host during the process of host entry and throughout the ensuing infection. Despite the high cost of infection and the low cost of avoidance, metamorph Cane Toads seem to lack effective parasite avoidance strategies.
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| 13. |
- Löwenborg, Kristin, et al.
(författare)
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Agricultural by-products provide critical habitat components for cold-climate populations of an oviparous snake (Natrix natrix)
- 2012
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Ingår i: Biodiversity and Conservation. - : Springer Science and Business Media LLC. - 0960-3115 .- 1572-9710. ; 21:10, s. 2477-2488
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Tidskriftsartikel (refereegranskat)abstract
- Populations of snakes and other reptiles are declining worldwide. Habitat loss and degradation is thought to be a significant factor in these declines, so to improve management strategies it is important to increase our understanding of reptilian habitat requirements. Modern agriculture is abandoning the tradition of gathering compost and manure in large heaps. Consequently these unusually warm environments are disappearing from the landscape. This may imperil populations of grass snakes (Natrix natrix) that rely on these anthropogenic heat sources to incubate their eggs. We conducted a relocation experiment to examine if eggs can develop successfully in other more natural environments that grass snakes potentially could utilize in the absence of manure heaps and compost piles. We found that hatching success was high (71 %) when we placed eggs in manure heaps and non-existent (0 %) when we placed them in potential ‘natural’ nests. Placement in compost piles resulted in intermediate (43 %) hatching success. Eggs in manure heaps hatched earlier than eggs in compost piles and thermal data from the nests showed that temperatures were higher and more stable in manure heaps than in compost piles and potential ‘natural’ nests. Jointly these results suggest that manure heaps generally provide a better nesting habitat than compost piles, attributable to thermal differences between the environments. Our findings facilitate improvement of current management strategies and have implications for conservation of oviparous reptiles in general.
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| 14. |
- Löwenborg, Kristin, et al.
(författare)
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Fitness disadvantages to disrupted embryogenesis impose selection against suboptimal nest-site choice by female grass snakes, Natrix natrix (Colubridae)
- 2011
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Ingår i: Journal of Evolutionary Biology. - : Wiley. - 1010-061X .- 1420-9101. ; 24:1, s. 177-183
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Tidskriftsartikel (refereegranskat)abstract
- Phenotypic traits of hatchling reptiles are strongly influenced by incubation regimes (e.g. of temperature and moisture), suggesting that maternal choice of suitable nest-sites should be under intense selection. Our laboratory incubation of 209 eggs (17 clutches) from wild-caught Swedish grass snakes (Natrix natrix) showed that scale abnormalities (half-scales on one side of the body, often reflecting lateral asymmetry in the number of ribs) occurred more frequently if eggs were incubated under cooler conditions. Especially at low incubation temperatures, individuals with scale asymmetries took longer to hatch than did symmetric conspecifics, were smaller in body length at hatching and were slower in trials of locomotor speed. Anti-predator tactics also covaried with scale asymmetry. These patterns suggest that individuals with asymmetric scales should have lower fitness and hence should rarely survive to adulthood in the wild. We tested this prediction by examining 201 field-collected snakes from museum collections. As predicted, scale asymmetries were seen primarily in small snakes, and rarely in larger animals. We interpret these data to suggest that scale asymmetries in this species offer an index of developmental instability and that fitness disadvantages to disrupted embryogenesis impose selection against suboptimal nest-site choice by females.
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| 15. |
- Löwenborg, Kristin, et al.
(författare)
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Grass snakes exploit anthropogenic heat sources to overcome distributional limits imposed by oviparity
- 2010
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Ingår i: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 24:5, s. 1095-1102
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Tidskriftsartikel (refereegranskat)abstract
- P>1. A lack of warm nest-sites prevents oviparous reptile species from reproducing in cool climates; such areas are dominated by viviparous species because sun-seeking pregnant females can maintain high temperatures for their developing offspring. 2. Our field and laboratory studies show that one oviparous species (the grass snake, Natrix natrix) escapes this cold-climate constraint (and hence, extends much further north in Europe than do other oviparous taxa) by ovipositing in a thermally distinctive man-made microhabitat (manure heaps on farms). 3. In the field, temperatures inside manure heaps averaged 30 center dot 7 degrees C, much higher than compost heaps (20 center dot 6 degrees C) or potential natural nest-sites under logs and rocks (15 center dot 5 degrees C). 4. In the laboratory, higher incubation temperatures not only hastened hatching, but also increased hatching success and modified the body sizes, colours, and locomotor abilities of hatchlings. Incubation temperatures typical of manure heaps (rather than alternative nest-sites) resulted in larger, faster offspring that hatched earlier in the season. 5. Thus, anthropogenic activities have generated potential nest-sites offering thermal regimes not naturally available in the region; and grass snakes have exploited that opportunity to escape the thermal limits that restrict geographic distributions of other oviparous reptile taxa.
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| 16. |
- Löwenborg, Kristin, et al.
(författare)
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How a thermal dichotomy in nesting environments influences offspring of the world's most northerly oviparous snake, Natrix natrix (Colubridae)
- 2012
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Ingår i: Biological Journal of the Linnean Society. - : Oxford University Press (OUP). - 0024-4066 .- 1095-8312. ; 107:4, s. 833-844
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Tidskriftsartikel (refereegranskat)abstract
- Temperature has a major influence on the rate of embryonic development in ectothermic organisms. While incubation experiments unambiguously show that constant high temperature accelerates development and shortens embryonic life, studies on the effect of fluctuating temperatures have generated contradictory results. Grass snakes (Natrix natrix) occur at latitudes and altitudes that are unusually cool for an oviparous reptile. In these cool climates females typically lay their eggs in heat-generating anthropogenic microhabitats that provide either a highly fluctuating (compost piles) or a relatively constant (manure heaps) thermal nesting environment. A laboratory experiment with fluctuating and constant incubation temperatures mimicking those recorded in such nests in the field showed that this nest-site dichotomy influences the development of the embryos, and the morphology and locomotor performance of the hatchlings. The incubation period increased at fluctuating temperatures and the fact that the rate of embryonic development showed a decelerating pattern with temperature suggests that periods of low temperature had a relatively larger influence on average development than periods of high temperature. Our study demonstrates how a dichotomy in the nesting environments available to female grass snakes in cool climates can affect variation in the duration of the incubation period and offspring phenotypes in ways that may have consequences for fitness.
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| 17. |
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| 18. |
- Tegelaar, Karolina, et al.
(författare)
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Ant-aphid mutualism : the influence of ants on the aphid summer cycle
- 2012
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 121:1, s. 61-66
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Tidskriftsartikel (refereegranskat)abstract
- There are few longtime studies on the effects on aphids of being tended by ants. The aim of this study is to investigate how the presence of ants influences settling decisions by colonizing aphids and the post-settlement growth and survival of aphid colonies. We conducted a field experiment using the facultative myrmecophile Aphis fabae and the ant Lasius niger. The experiment relied on natural aphid colonization of potted plants of scentless mayweed Tripleurospermum perforatum placed outdoors. Ants occurred naturally at the field site and had access to half of the pots and were prevented from accessing the remainder. The presence of winged, dispersing aphids, the growth and survival of establishing aphid colonies, and the presence of parasitoids were measured in relation to presence or absence of ants, over a period of five weeks. The presence of ants did not significantly influence the pattern of initial host plant colonization or the initial colony growth, but ant-tended aphids were subject to higher parasitism by hymenopteran parasitoids. The net result over the experimental period was that the presence of ants decreased aphid colony productivity, measured as the number of winged summer migrants produced from the colonized host plants. This implies that aphids do not always benefit from the presence of ants, but under some conditions rather pay a cost in the form of reduced dispersal.
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