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You are here: Home / 2019 / Archives for July 2019

Archives for July 2019

What our animals are doing this month…

July 30, 2019 by admin

What our animals are doing this month… August 2019

August is the month that young grass snakes are likely to emerge from their eggs.  Previously in the year, gravid female grass snakes will have been seen basking more intensively than other grass snakes as they developed their eggs. During this time, females will fast for roughly 45 days whilst eggs develop and are laid.

Grass snakes usually just lay one clutch in a breeding year and do not necessarily reproduce on an annual basis. Eggs are laid in warm, secluded areas such as compost heaps, manure piles, old mammal holes, log piles or under rocks. These eggs need to be incubated anywhere from 22 days to 45 days depending on the environmental conditions. Areas of higher temperature have shown beneficial results for the numbers of eggs developing, with temperatures of 210C to 310C being preferred.

An average clutch size of eggs for a grass snake is 30 eggs, however many females may lay communally with others which can result in areas with thousands of eggs being incubated together.

By August hatchlings should emerge, measuring 15-20cm with the same identification features as adult grass snakes. Hatchlings use an ‘egg tooth’ to escape their egg by breaking the shell – this tooth is lost shortly after emerging.

Remember to report your sightings (including egg sightings) with our FREE Dragon Finder app.

Figure 1: Juvenile grass snakes can be easily identified being miniature versions of adults

Filed Under: Uncategorized Tagged With: Croaking Science, grass snakes

Croaking Science: Unisexuality- an alternative reproductive strategy

July 30, 2019 by admin

Approximately 90 vertebrate species are known to exist as unisexual populations, that is, consisting of reproducing females (Lampert & Schartl, 2010). All of these are restricted to fish, amphibian and reptile species (Figure 1). An all-female reproducing population has advantages since every individual can carry young so the population has the potential to grow at a faster rate than bisexual populations, where the male only donates sperm and does not produce offspring. Since this has a distinct advantage it is perhaps unusual that unisexual populations are so rare. However, the main cost of being unisexual is the loss of genetic recombination which occurs in male and female bisexual populations. This is crucial in providing genetic stability, preventing accumulation of mutations and providing opportunities for adapting to a changing environment. Therefore, unisexual species do not occur widely amongst vertebrates.

Figure 1. The Caucasian rock lizard is one of a few lizards which are unisexual
[Photo credit: Alastair Rae, https://commons.wikimedia.org/wiki/File:Caucasian_Rock_Lizard_(34598190795).jpg]

Unisexual reproduction is often referred to as parthenogenesis, which is “reproduction in the absence of fertilization of the egg” (Lampert & Schartl, 2010). However, there are different forms of parthenogenesis which do allow some genetic exchange. True parthenogenesis occurs in females in the complete absence of males. This is incredibly rare and is known only from a handful of vertebrate species. However, one other type of parthenogenesis, known as gynogenesis, occurs when male sperm is used to trigger development of the female’s embryo. In this circumstance, the female does not incorporate any of the sperm’s genetic material and she uses all of her own so the sperm’s genome is redundant. However, in some situations, known as kleptogenesis, the female may incorporate some of all of the sperm’s genome thus resulting in offspring that have, 2, 3 or 4 times the amount of genetic material (diploid, triploid or tetraploid respectively) (Bogart et al., 2007). Since they ‘steal’ gametes of sexual species for their own reproduction, they are considered to be sexual parasites of their (usually parental) host species (Mikulíček et al., 2014). A third type of parthenogenesis is hybridogenesis where the eggs of a unisexual female are fertilised by the sperm of a closely related bisexual male. However, this genetic material is only incorporated into the new genome for one generation and is excluded when this female produces her own eggs (Lambert et al., 2010).  Therefore, only maternal genes are passed onto subsequent generations. All these forms of parthenogenesis result in the inclusion of ‘fresh’ genetic material into the female thus improving the fitness of populations and increasing their robustness to resist diseases.

Figure 2. Four species of Ambystoma salamander which may be included in the nucleus of unisexual individuals. [Photo credit: Bogart et al., 2007.]

Two main groups of amphibians are known to exhibit unisexuality. Unisexual mole salamanders (genus Ambystoma), occur in North America and generally have between two and five times the normal complement of genetic material compared to bisexual Ambystomid salamanders (Figure 2). These Ambystomid unisexual individuals are the oldest known group of unisexual vertebrates, having occurred for over 5 million years (Gibbs & Denton, 2016). The DNA in the nucleus of unisexual individuals is usually composed of genetic material from several species including: the blue spotted salamander (Ambystoma laterale), Jefferson salamander (A. jeffersonianum), small-mouthed salamander (A. texanum) and tiger salamander (A. tigrinum). This leads to a large range of possible genetic combinations with genetic material from the blue spotted salamander being present in most unisexual individuals. Female unisexual salamanders require sperm from a bisexual salamander species which are living in the same area to initiate reproduction. However, they can then either use the sperm solely to activate egg development (i.e. gynogenesis) or incorporate the sperm genome into the resulting offspring (Bogart et al., 2007). If genetic material from the sperm is used during reproduction, either the DNA is retained, resulting in the offspring with additional genetic material, or it is replaced. In a recent study, Gibbs & Denton (2016) studied the genetic exchange in unisexual populations of Ambystomid salamanders to try and explain how unisexual populations have persisted in the environment for 5 million years. They found that unisexual individuals gain enough genetic material through the occasional process of obtaining DNA from males to allow populations to remain robust and able to withstand environmental change. Therefore these individuals gain all the advantages of being unisexual, with also some of the advantages of sexual reproduction i.e. genetic mixing.

Figure 3. Two edible frogs (Pelophylax esculentus). [Photo credit: Awewewe,]

One of the well-known breeding systems involving hybridogenesis is that of the water frog (Pelophylax esculentus) complex (Ranidae), widely distributed in Europe, which has considerable variation in types of hybridogenesis (Figure 3). The Pelophylax esculentus complex consists of two parental species, the marsh frog (P. ridibundus) and pool frog (P. lessonae), and their hybridogenetic hybrid the edible frog (P. esculentus). Edible frogs usually contain genetic material from both parental species. In most of its range, the edible frog reproduces hybridogenetically with the pool frog. However, during reproduction the pool frog genome is lost in the eggs and sperm. Therefore, pool frog DNA is not passed down to subsequent generations and the edible frog is considered a sexual parasite (Christiansen et al., 2005). However, many variations of this mating system occur across the species’ range. In most cases, female edible frogs will use the genetic material from the male, but it is not fully incorporating it into its genome. Due to the unusual genetic combining during hybridogenesis the presence of edible frogs can result in loss of the parental pool frog and marsh frog genotypes and is a potential conservation problem when it occurs in these populations.

Overall, unisexuality in amphibians represents a unique form of reproduction that has remained evolutionarily stable for several million years through occasional genetic mixing from the same or closely related species. Ambystomid salamanders and water frogs have proved highly successful at unisexual reproduction which is otherwise a rarely used breeding strategy amongst vertebrates.

References

Bogart, J.P., Bi, K., Fu, J., Noble, D.W.W. & Niedzwieckim, J. (2007) Unisexual salamanders (genus Ambystoma) present a new reproductive mode for eukaryotes. Genome, 50: 119–136.

Christiansen, D.G., Fog, K., Pedersen, Bo V. & Boomsma, J.J. (2005) Reproduction and hybrid load in all-hybrid populations of Rana esculenta water frogs in Denmark. Evolution, 59 (6): 1348–1361.

Gibbs, H.L., & Denton, R.D. (2016) Cryptic sex? Estimates of genome exchange in unisexual mole salamanders (Ambystoma sp.). Molecular Ecology, 25: 2805–2815.

Lampert, K.P. & Schartl, M. (2010) A little bit is better than nothing: the incomplete parthenogenesis of salamanders, frogs and fish. BMC Biology, 8: 78-80.

Mikulíček, P., Kautman, M., Kautman, J. & Pruvost, N.B.M. (2014) Mode of hybridogenesis and habitat preferences influence population composition of water frogs (Pelophylax esculentus complex, Anura: Ranidae) in a region of sympatric occurrence (western Slovakia). Journal of Zoological Systematics & Evolution Research. doi: 10.1111/jzs.12083.

Filed Under: Uncategorized Tagged With: Croaks, reproduction

Heatwave Advice for Amphibians & Reptiles

July 24, 2019 by admin

During periods of hot weather when temperatures exceed 30°C, amphibians are at increased risk of dehydration and desiccation. It is normal during these periods for amphibians to either take refuge in water bodies or seek sheltered and cool terrestrial habitats. Common frogs and newts may still be in ponds so are able to withstand the high temperatures. However, common toads are largely terrestrial during the summer so finding suitable places for shelter is crucial. Habitats such as loose damp soil, leafy shrubs, logs and piles of dead leaves are all ideal habitats for amphibians such as toads, newts and frogs. You can help amphibians in your garden in several ways:

  • If you have a pond, ensure that there are some areas of shade. If your pond is exposed you could create shade by placing pots containing plants around the southern perimeter of the pond. Also, ensure there are a range of submergent and emergent plants in your pond which will also provide cover. See Just Add Water for more information.
  • Provide areas of loose, damp soil, preferably within shrubs or undergrowth. Often amphibians will burrow underground to avoid the heat. Regularly watering areas of soil can help keep these cool and damp.
  • Keep an area of your garden overgrown with weeds, shrubs and long grass as this will provide valuable shaded areas for amphibians.
  • Create an area of rocks and stones as amphibians often seek refuge within cool and dark crevices.
  • If you carry out some gardening activities, create a compost heap which will provide a refuge for amphibians, and also reptiles. See our wildlife gardening tips for more information

Reptiles are generally much better adapted to the hot and dry weather compared to amphibians as they have less permeable skin. Reptiles such as common lizards, grass snakes and adders will thrive in hot conditions and be highly active as they hunt their prey.

If you have any questions about amphibians or reptiles, take a look at our FAQ’s page here.

Photo by Ben Killick

Filed Under: Uncategorized

Help Froglife win a National Lottery Award.

July 24, 2019 by admin

Froglife have reached the final of the 25th Birthday National Lottery Awards beating over 700 other charities. We need your help to win £10,000 which will greatly assist us in continuing our vital work to conserve amphibians and reptiles.

Please follow this link and vote for us. Voting closes at midnight on 21st August. Please see the poster below for more information.

Filed Under: Uncategorized

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