Evolutionary prosperity

By | Science & Technology
Spicebush swallowtail caterpillar (Papilio troilus).Credit@flickruser:MichealHodge

The success of insects has been the focus of a study, which highlights physiological processes within insects which may have led to an increased efficiency in transport of sugars between cells. These adaptations are thought to be a product of the insects’ inherent reliability on environmental temperature to maintain internal body temperatures.

Insects live in all environments and represent over a million species or half of all known living organisms. Insects are invertebrates and develop and grow by moulting the external layers of the exoskeleton and may even go through a metamorphosis stage. The organisms originated in the paleozoic period 541 to 525 million years ago a period of rapid diversification of life on earth, when life originally was present only in the oceans and transitioned to land. Invertebrates appeared in the Cambrian period when primitive fish later evolved into land organisms. This era ended with the largest extinction in earth’s history; the Permian Triassic extinction event, the earth took 30 million years to recover although ocean life may have recovered more rapidly. The survival of insects is therefore an innovative feat and how this was managed has been a focus of attention for scientists.

A study by Finn and colleagues in the journal nature communications aimed to uncover the physiological advantage shared by insects. The team focussed on the glycerol transport between cells possessed by insects, facilitated in other organisms by aquaglyceroporins a type of protein that develop pores in the membranes of cells, despite being absent in insects. These membranes function as channels for the purpose of transferring water and solutes through the membrane and the team aimed to find how glycerol transport took place in insects with the absence of aquaglyceroporins.

Holometabolan insects specifically go through distinctive larval, pupal and metamorphosis stages, the team observed a more efficient form of glycerol transporter may have evolved inherent to these insects’ genetics. The team did this by combining phylogenetic (the ancestral evolutionary branching process) and functional studies and found a specific water channel within insects evolved to change this channel physiologically. This may mean holometabolan insects possessing this function separated from the ancestral branch of aquaglyceroporins. The team demonstrated this by using insects genetically altered with distantly related aquaporins to show a single mutation in a water channel transformed it into a glycerol transporter. This process is termed neofunctionalisation where a gene acquires a new function following genetic duplication which may have been absent in an ancestral gene.

Explanations as to why this glycrerol transporter may have incurred an advantage may have been documented in previous studies showing how holometabolan insect species aim to accumulate large quantities of glycerol and how this may be an adaptive response to dehydration and freezing temperatures. Similar adaptive responses may be shared by organisms capable of withstanding extreme desiccation, this ability may be thought to occur because of the metabolism of certain sugars, conversely organisms unable to synthesise particular sugars are challenged to survive even under mild desiccation. This glycerol accumulation may be at its highest level during the metamorphosis stage when the insect might be more vulnerable. Phylogenetic findings suggest these adaptations may also have taken place during glaciation periods of the Phanerozoic eon, showing a direct link between the two events.

The findings suggest the neofunctionalised glycerol transporting genes are a unique alteration which establishes hexapods as a new species and may be the foundation of the species success. Specifically, a single mutation in water selective membrane converted the membrane into a glycerol transporter, this may be an important innovation, which led to the creation of the hexapoda species. The functional advantages hexapods have obtained may have helped the species in times of cold climate and low water availability throughout long periods of evolution. These adaptations may have been essential to the survival of insects considered poikilotherms, as body temperature is dependent on environmental temperature. The pupal stage where metamorphosis takes place may only have emerged with this change in function of the glycerol transporter gene, creating the possibility for the origin of species like the butterfly, an example of an advantageous evolutionary change.

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