A hypomorphic cystathionine ß-synthase gene contributes to cavefish eye loss by disrupting optic vasculature

Vestigial structures are key indicators of evolutionary descent, but the mechanisms underlying their development are poorly understood. This study examines vestigial eye formation in the teleost Astyanax mexicanus, which consists of a sighted surface-dwelling morph and multiple populations of blind cave morphs. Cavefish embryos initially develop eyes, but they subsequently degenerate and become vestigial structures embedded in the head. The mutated genes involved in cavefish vestigial eye formation have not been characterized. Here we identify cystathionine ß-synthase a (cbsa), which encodes the key enzyme of the transsulfuration pathway, as one of the mutated genes responsible for eye degeneration in multiple cavefish populations. The inactivation of cbsa affects eye development by increasing the transsulfuration intermediate homocysteine and inducing defects in optic vasculature, which result in aneurysms and eye hemorrhages. Our findings suggest that localized modifications in the circulatory system may have contributed to the evolution of vestigial eyes in cavefish.

A critical survey of vestigial structures in the postcranial skeletons of extant mammals

In the Mammalia, vestigial skeletal structures abound but have not previously been the focus of study, with a few exceptions (e.g., whale pelves). Here we use a phylogenetic bracketing approach to identify vestigial structures in mammalian postcranial skeletons and present a descriptive survey of such structures in the Mammalia. We also correct previous misidentifications, including the previous misidentification of vestigial caviid metatarsals as sesamoids. We also examine the phylogenetic distribution of vestigiality and loss. This distribution indicates multiple vestigialization and loss events in mammalian skeletal structures, especially in the hand and foot, and reveals no correlation in such events between mammalian fore and hind limbs.

Vestigial Biological Structures

Lists of vestigial biological structures in biology textbooks are so short that some young-Earth creationist authors claim that scientists have lost confidence in the existence of vestigial structures and can no longer identify any verifiable ones. We tested these hypotheses with a method that is easily adapted to biology classes. We used online search engines to find examples of 21st-century articles in primary scientific literature in which biological structures are identified as vestigial. Our results falsify these creationist hypotheses and show that scientists currently identify many structures as vestigial in animals, plants, and single-celled organisms. Examples include not only organs but also cells, organelles, and parts of molecules. Having students repeat this study will give them experience with hypothesis testing, introduce them to primary scientific articles, and further their education on vestigial structures.

Bidder's organs: Bufonid by-products of the evolutionary loss of hyperfecundity

Bidder's organs in both male and female bufonids are hypothesized to represent a transitory state in an evolutionary transformation from extensive, hyperfecund ovaries to smaller, less fecund ones-a transformation that other families of anurans experienced in forms now long extinct. Some members of the genus Bufo retain considerable hyperfecundity, but in derived species of Bufo and genera of Bufonidae a spectrum of ovarian reduction exists. In those groups, Bidder's organs normally persist, always in males and often in females, as an undifferentiated ovaroid or ovary in a non-functional transition between the ancestral state and modification as part of the fat body. The organs are gynomorphs in males and highly variable as vestigial structures, but may well have endocrinogenic functions in both sexes although gametogenic functions in nature have been lost in males. Presence of Bidder's organs is a derived condition in the context of anurans as a whole, but primitive within the family Bufonidae.