Kyoto University analyzes the lack of size variety in hares and bunnies.
Next to feline videos, enjoying cuddly and small rabbits is most likely among the most popular internet activities. Plus they appear in literature in addition to in traditional folklore covering many cultures, thanks likely to the reality that bunnies live on every continent other than Antarctica.
Regardless of their universality, lagomorphs– including pikas, bunnies, and hares– are rather limited in their size diversity. Compare this to their evolutionary sisters, the rodents, which vary in size from the four-gram pygmy mouse to capybaras weighing as much as 50 kilograms.
So why dont we see rabbits matching the sizes of horses?
To answer this question, a research group led by Kyoto Universitys Primate Research Institute investigated the fossil record and evolutionary history of lagomorphs. In a study in the journal Evolution, the team reports that larger herbivore competitors were one evolutionary restriction restricting bunnies size.
Representation of both biotic (Red Queen) and abiotic (Court Jester) models of lagomorph body size development. Metaphorically unfolding as an evolutionary play in an eco-friendly theater as might have been pictured by ecologist G. Evelyn Hutchinson. Credit: Adrienne Stroup
” The biggest living wild lagomorphs weigh just about 5 kg on average, a tenth of the biggest living rodent, the capybara,” states first author Susumu Tomiya.
” But some breeds of domestic rabbits and other extinct species can weigh up to 8 kg. We were amazed by this, and so started to examine what sort of external forces keep wild lagomorphs throughout the world from evolving larger body sizes.”
The researchers started by analyzing ecological elements, finding that the body sizes of ungulates– hoofed animals– are the most prominent predictor.
” We next compared just how much energy is utilized by populations of ungulates and lagomorphs relative to their body sizes,” continues Tomiya, “discovering that lagomorphs weighing more than 6 kgs are energetically at a competitive drawback to ungulates of the exact same size.”
The team last but not least went through the lagomorph fossil record in North America, discovering that the best predictor for optimum body size was that of the tiniest simultaneous ungulate.
” We see this pattern today throughout various eco-regions, suggesting that there is an evolutionary ceiling placed on lagomorphs by their ungulate rivals,” describes Tomiya.
These findings recommend that competitive biotic procedures can play an essential function in forming the evolutionary history of mammalian orders, acting in hand with abiotic processes such as modifications in environment.
” A continuous argument in evolutionary biology concerns whether ecological or biological processes are more vital in shaping biological variety,” specifies Tomiya, “as defined by the red queen and court jester hypotheses.”
” For a long time, the court jester model– ascribing diversity to abiotic forces such as the environment– has been dominant, due to the trouble of studying biological interactions in the fossil record.”
The teams results reveal that biotic interactions do play a crucial role in directing the evolutionary trajectories of some types, within the bigger context of abiotic impacts.
Recommendation: “Why arent hares and bunnies bigger?” by Susumu Tomiya and Lauren K. Miller, 18 February 2021, Evolution.DOI: 10.1111/ evo.14187.