A Plethora of Senses

This chapter discusses the variety of animal senses, how they work, what they are used for, and why such a staggering array of senses exists in nature. The senses found across animal species, and even among individuals of the same species, vary according to many factors. Animal senses are carefully refined through evolution and development for the things that matter most to them. To accomplish the numerous tasks every individual must perform, the senses are tuned to work best in the habitats where the creature lives and to acquire the best available sources of information. Sometimes, one or more of the senses are exquisitely tuned to a few crucial tasks an animal must perform in order to survive and reproduce successfully. Investment in different senses can also be flexible depending on the conditions under which an animal grows up. Through adaptation over many generations, species like blind cave fish can decrease investment in one sense in favour of another, but individual animals can also do this during their lives.

A new species of the cave-fish genus Lucifuga (Ophidiiformes, Bythitidae), from eastern Cuba

Recently, a barcoding study and a molecular phylogenetic analysis of the Cuban species of the cave-fish genus Lucifuga Poey, 1858 revealed the existence of different evolutionary lineages that were previously unknown or passed unnoticed by morphological scrutiny (i.e., cryptic candidate species). In the present study, Lucifuga gibarensis is described as a new species restricted to anchialine caves in the northeastern karst region of the main island. The species was earlier described as a variety of Lucifuga dentata, but since the name was introduced as a variety after 1960, it is deemed to be infrasubspecific and unavailable according to the International Code of Zoological Nomenclature Art. 15.2. The new species differs from L. dentata by pigmented eyes vs. eyes absent and lack of palatine teeth vs. present. Lucifuga gibarensis seems to be most similar to the Bahamian species L. lucayana by showing pigmented eyes, 13 or 14 precaudal vertebrae and ten caudal fin rays. However, differs from it by a larger size of the pigmented eye (1.1–1.9 vs. 0.9–1.0% SL) and number of posterior lateral line neuromasts (30–33 vs. 34–35).

The role of selection in the evolution of blindness in cave fish

The forces driving regression of biologically functionless traits remain disputed. There is ongoing debate regarding whether selection, as opposed to disuse and neutral mutations, is involved in this process. Cave species are of particular relevance for study in this regard because in continuous darkness all traits that depend on information from light, such as eyes, dark pigmentation and certain behaviours, abruptly lose their function. Recently, strong selection driving reduction has again been proposed, which relied on modelling analyses based on assumptions such as immigration of surface alleles into the cave forms or no fitness difference existing between Astyanax surface and cave fish. The validity of these assumptions, often applied to reject neutral processes in functionless traits, is questioned in this review. Morphological variation in a trait resulting from genetic variability is typical of biologically functionless traits and is particularly notable in phylogenetically young cave species. It is the most evident indicator of loss of selection, which normally enforces uniformity to guarantee optimal functionality. Phenotypic and genotypic variability in Astyanax cave fish eyes does not derive from genetic introgression by the surface form, but from regressive mutations not being eliminated by selection. This matches well with the principles of Kimura’s neutral theory of molecular evolution.

Adaptations to Subterranean Life

The loss of characters, especially eyes and pigment, in subterranean animals has attracted the attention of biologists since their first discovery centuries ago. Adaptationist ideas with regard to subterranean organisms were originally developed, not in connection with loss of eyes and pigment, but rather in connection with constructive changes such as appendage elongation and elaboration of extra-optic sensory structures. Three studies of adaptation epitomize adaptation as it applies to subterranean species. In Poulson’s study of life history and metabolic and neurological changes in cave fish, his basic approach was comparative, using related surface-dwelling species. Using quantitative genetics, Culver and colleagues studied the amphipod G. minus, focusing on the adaptation to the darkness of caves. Jeffery and colleagues focused on the causes of eye and pigment degeneration in the Mexican cavefish A. mexicanus. Using an array of techniques, they demonstrated the critical role pleiotropic selection plays.

AN OVERVIEW ON THE SUBTERRANEAN FAUNA FROM CENTRAL ASIA

Survey of the aquatic subterranean fauna from caves, springs, interstitial habitat, wells in deserts, artificial tunnels (Khanas) of five countries of the former URSS (Kazakhstan, Kyrgyzstan, Tadjikistan, Turkmenistan, Uzbekistan) located far east the Caspian Sea. The cave fauna present some originalities: - the rich fauna of foraminiferida in the wells of the Kara-Kum desert (Turkmenistan); - the cave fish Paracobitis starostini from the Provull gypsum Cave (Turkmenistan); - the presence of a rich stygobitic fauna in the wells of the Kyzyl-Kum desert (Uzbekistan); - the rich stygobitic fauna from the hyporheic of streams and wells around the tectonic Issyk-Kul Lake (Kyrgyzstan); - the eastern limit of the European genus Niphargus from the sub-lacustrin springs on the eastern shore of the Caspian Sea (Kazakhstan); - the presence of cave fauna of marine origin. Approximately 96 stygobionts, 9 stygobionts/stygophiles and 3 troglobionts are recorded.