Habitat and climatic variations impact on the population of the Capr velvet worm on the South African Cape peninsula and surrounding mountain area

A few weeks ago I was sitting in on a Masters Research proposal on genetic variation in invertabrate taxa on Banks Peninsula. By chance a famous New Zealander was also attending this proposal,

Ruud with a weta on his face!

who goes by the name Ruud Kleinpaste! If you don't know he is an iconic Kiwi personality off the T.V. show 'Buggin with Rudd'. He asked the person presenting there research ideas about an interesting group of invertabrates called the Onychophora (Velvet worms) found worldwide, and if he had come across any of them in his sampling. This person had not, as they are a interesting group (it has a crazy biology!) dating back to the Cambrian period 500 million years ago! So once I had decided to do a blog on insect phylogeography, it only seemed right that I investigate this group. This lead me to a paper showing how a velvet worm species biology, has influenced it's crytic evolution in a dynamic geological and climatic landscape.

First I should describe this creature of anicent proportions and what makes it so bizarre!

The mighty velvet worm!

Its a segmented invertabrate, with a flattened cylindrical body. It moves very slowly using its lobopods (stub feet) by expanding and contracting internal muscles in each lobopod. Each foot has a pair of retractable, sclerotised (hardened) chitin claws which are where its scientific name is derived: 'Onycho' 'phora' meaning "claws" and "carry" respectively, and are used to gain firm grips on uneven terrain. They are soft bodied creatures with a fluid-filled body cavity acting as a hydro skeleton, which is similar in unrelated soft bodied animals like worms. It respires via its whole body surface via diffusion. It lives in preferably dark environments with high air humidity and is found in tropical habits in the temperate zone within the South hemisphere. Due to there body make-up and slow movement habits they are night active to avoid desiccation (drying up) during the day time. They have oral papillae (slime glands) on the side of their head which is used to contain, then excrete slime onto approaching predators as defence or prey of interest.

For a more detailed description of velvet worms which I have only summarised above, go to this link: http://en.wikipedia.org/wiki/Onychophora#Conservation_status

The paper of interest is called; Phylogeography of the Cape velvet worm (Onychophora: Peripatopsis capensis) reveals impact of Pliocene and Pleistocene climatic oscillations on Afromontane froest in Western Cape, South Africa

The study site is on the south-western Cape, more specifically Cape Floristic Region (CFR) with a history of an early Miocene period (5-23mya) with a characteristic subtropical rainforest making up most of the vegetation. However the climate changed during the Pliocene era (2-5mya) amplifying the east-west rainfall gradient as mountains began forming in the south-eastern Africa making west CFR more arid winter only rainfall climate. The east contrastingly had year round rainfall. The current topography is shown in the below picture showing the molecular results based on the isolated habitats.

The afromontane forest was once one large connected forest. But aridification that occurred during the Miocene/ Pliocene separated this forest in discontinuous fragmented forests patches.With the two main types consisting of southern afromontane forest and southern coastal forest. This lead them to 3 main hypothesise (1) P.capensis will show a genetic history mirroring the paleogeography (isolation of habitat over time) due to it's specificity to habitat/ low dispersal; (2) The physical barriers of low lying coastal plains and lack of forest connectivity lead to this isolation also and (3) Increasing genetic differentiation should be observed moving along a west-to-south-easterly trajectory as the south-eastern part of the Cape Fold mountains have historically had a larger annual rainfall with larger forest patches creating more habitat heterogeneity (intra forest fragment variation/ ecotypes).

Specimens of P.capensis were collected from many sites over the Southern Cape. They were collected from forest floor litter and decaying plant material (there preferred habitat). A minimum of one specimen to a maximum of 10 were collected from 21 different sites in the western and southwestern cape regions of the western Cape Province of South Africa. Conventional DNA analysis methods were used to extract, amplify, sequence and analyse the sample DNA data. Refer to the paper for in-depth methods of DNA analysis if sort of thing interests you!

The results produced clear findings which eluded to the fact that their has been genetic differentiation. The phylogenetic tree produced showed that there were 3 genetically variable and distinct clades of P.capensis. Clade A is the Cape Peninsula population, which is separated by the Cape Flats and mountains from Clade C, the Theewaterskloof-Overstrand population. Furthermore Clade C is separated from Clade B which is the Overberg population, by the Breede River-valley and adjacent mountain ranges. These separations are in the form of habitat isolation due to geological change over time. The Cape flats is a shrub dominated and nutrient poor ecosystem, which has been shown in past studies to also limit gene flow between other invertebrate groups! In the case of P.capensis this habitat is less desirable to live in as there is less woody detritus and leaf litter to live in. It is also susceptible to desiccation in this habitat as it is more arid than the afromontane forest of the Cape Peninsula. The Breede River-valley produces unique abiotic conditions creating a semi-arid environment, with a multitude of variable soils (e.g. sandy, aeolian, acidic, alluvial, clay and loam) with only 270mm rainfall per annum. These unique condition are not suited for forest growth and therefore there is no dispersal pathway between Clades B and C, leading to this genetic differentiation. These results are consistent with the first and second hypothesis of the authors!

This is a phylogenetic tree showing the three clades of velvet worm based on variation in the sequences on the CO1 gene

Within habitat heterogeneity was different between all three clades. This means there is a larger amount varying habitats in certain clades, leading to a greater population structure and genetic variability. Clade A shown in red on the above Fig 3 had the lowest haplotypic diversity (inter clade genetic variation), as the habitat in the region was relatively continuous and was relatively consist (no large variation in topography or climate). Clade B had the highest level of haplotypic diversity as the Overberg region had many fragmented areas of forest habitat meaning dispersal by P.capensis is greatly limited. Clade C was the largest in area with a varying climate. Rainfall varied from only in winter on the western part of Theewaterskloof-Overstrand to year round in the south east. Also as the Cape mountains (where a large proportion of afromontane forest grows) lies in this area there is a high amount of topographic heterogeneity. It was suggested that this area has had a long evolutionary history with 3 distinct haplotypes arising between the most variable and extreme environments due to evolution at the meta population level. The level of habitat heterogeneity varying from low in the west (Clade A) to highest in the south east (Clade C)! The authors again were able to validate their third hypothesis.

This paper is a really cool way to show how habitat can influence invertebrate species interactions in a dynamic environment. It provides insight that allows people to realise that; hey what we thought was one well dispersed species is possibly 2 or even 3! This could impact the taxonomic classification of species as many areas in the world will have similar patterns of evolution and population isolation occurring.

Thanks for reading my first blog post!!! (I hope you could follow most of it!)

This is the link to the paper:http://onlinelibrary.wiley.com.ezproxy.lincoln.ac.nz/doi/10.1111/j.1420-9101.2012.02482.x/pdf

 
If you wanna find out what the bug man is all about i suggest you check out the links below :D

http://www.youtube.com/watch?v=UefNF-65hTA&list=PL3562ECF090AF7264 

(Just copy and paste the link this stupid blog is messing with my formatting :O)