What in the World Am I Looking At!?

Take a look at this animal.

Photo of an adult Saiga

Photographer: Unknown

I assume that most of you are looking at this, asking yourselves; “But...WHY???” I know I was when I first saw it anyway.

This rather interesting looking animal is called a Saiga (Saiga t. tatarica) and it has evolved one of the most extraordinary noses (or proboscis) among the mammalian kingdom. (Frey, et al. 2007) The Saiga is a relatively young species that appear to have originated in central Asia in the late Tertiary (Pliocene) or early Quaternary (Pleistocene). (Frey, et al. 2007) Recent individuals are quite morphologically similar to fossils from Pleistocene Saigas, and so reconstruction of the evolution of this nose is difficult. (Frey, et al. 2007) In fact, the biological role of this nose has not even been fully explained. The most accepted hypothesis is that this contraption initially evolved to filter out dust particles from inhaled air when large herds of these species migrate and kick you copious amounts of dust. (Frey, et al. 2007) The video below shows just how much dust is kicked up during their cross-country migrations.

This type of locomotion (called the ‘amble’) is most energetically advantageous across an open flat semi-arid steppe environment, and it involves the neck being kept horizontal, meaning that the head is almost permanently immersed in a dust cloud. (Frey, et al. 2007) It has been suggested that a selection pressure for the evolution of a dust filter has led to the extraordinary size and shape of these noses in both sexes. (Frey, et al. 2007)

Diagram showing the anatomical structure of the Saiga proboscis. This includes the lateral vestibular recess, alarobasal fold, nasal septum and the vocal tract. The nasal passage is indicated in red and the oral passage is indicated in blue. (Frey, et al. 2007)

There is also a sexual dimorphism evident in nose sizes, as males have a longer proboscis, especially when performing a rut. (Frey, et al. 2007) This display occurs from December to January, where male establish territories and gather (sometimes up to 50) females, defending them in severe fights against rival males. (Frey, et al. 2007)

Diagram showing the nose extension in an adult male saiga during the rut. The image on the top is the resting position and on the bottom is the calling posture. (Frey, et al. 2007)

Females also call, but their noses are often more relaxed during this process, and it is used for a different reason, most likely to call to their young. (Frey, et al. 2007) Another suggested reason for the evolution of this nose is heat loss. The environment these animals live in can be as hot as 50^oC, which is enough to cause brain damage in most animals, however the passage of air through the proboscis cools down the inhaled air and in turn cools down the body of this amazing animal. (Frey, et al. 2007)

The following is a hypothetical step-by-step model for the evolution of the Saiga nose, taking into consideration is specialization for vocalizing and the ecological constraints found in dry-steppe environment. (Frey, et al. 2007)

1. Increasing use of the amble as a mode of fast locomotion by a smaller-sized bovid promoted the initial evolution of the unique nose, with slit-like nostrils
2. A low head position is advantageous for ambling (better extension of forelimbs through greater freedom of shoulder musculature). However, due to the large dust clouds produced by this mode of transport, the slit-like nostrils have to be opened more widely. This mean means that small nasal vestibulum is more susceptible to getting clogged with dust, causing a reduced efficiency of breathing (tradeoff!)
3. This is followed by the evolution of slightly larger nasal vestibula, at the expense of the nasal cavity proper in both sexes. These changes lead to a large difference in the dimensions of the nasal cavities compared to a typical bovid nose.
4. These transformations may have led to a reduced efficiency of counter-current exchange of heat and water vapour effected by the respiratory region, and so the advantages of the derived nose structure must overcompensated those disadvantages (another trade-off!)
5.  The increasing demand for getting rid of mucus and dust from the nasal vestibulum caused regular forced expirations through the nose, which lead to a preferential calling through the nose rather than through the mouth in both sexes.
6. Increasing use of the nasal airway by adult males during rutting calls instigated the evolution of sexual dimorphism by mechanisms of sexual selection (a mechanism discussed in my previous blogs)
7. Nasal, instead of oral, roaring was favoured by selection. Roaring loudly through the nose signals an exaggerated body size to conspecifics when compared to roaring through the mouth (a constraint to the further reduction of the nasal cavity proper and enlargement of the nasal vestibulum means the acoustic signal is an honest indicator of body size which provides reliable information for rivals as well as females).

I realise this post is a bit off topic, considering my blog is about trade-offs and constraints. However, I mentioned in my first post how intrigued I am by the mechanisms that cause species to develop weird and wonderful body parts and behaviours that just don’t seem to make sense at first glance. The Saiga is a perfect example of a creature that, when first seen, evokes feelings of curiosity and wonderment as to how and why something has evolved like this. Upon further investigation, as we can see, there is a very legitimate reason for having such a ridiculously large nose!

This amazing creature is unfortunately critically endangered due to high levels of poaching, and their numbers have declined by 95% in just the past 15 years. (The Saiga Conservation Alliance, 2014) The Saiga Conservation Alliance aims to restore populations and save them from imminent extinction. They welcome support from the public. Their link is: http://www.saiga-conservation.com/ if you are interested in further information.

References:

• Frey, R., Volodin, I. & Volodina, E. 2007, "A nose that roars: anatomical specializations and behavioural features of rutting male saiga", Journal of Anatomy, vol. 211, no. 6, pp. 717-736.
• The Saiga Conservation Alliance, 2014, 25^th May 2014 <http://www.saiga-conservation.com/>
• Viewed 23^rd May 2014 <http://www.listoid.com/list/18>