Contrasting feeding habits of post-larval and adult Astyanax cavefish

Abstract

The subterranean environment is often described as "extreme" and food poor. Laboratory experiments have shown that blind Mexican tetra Astyanax mexicanus (De Filippi, 1853) cavefish are better at finding food in the dark than surface fish. Several morphological and behavioural attributes that could foster this obvious adaptive response to cave environments have been described. Nonetheless, it is currently unknown what young cavefish actually eat in their natural cave environment. Our results from the Pachón cave in México during the dry and rainy season show that fry are efficient predators in their natural cave environment. Their primary food item is aquatic crustaceans. The guts of post-larval, pre-juvenile stage individuals (n=9) contained an average of 17.9 water fleas (Cladocera), copepods, ostracods, and isopods. Thus, the fry in this cave are well-fed. The Pachón cave environment does not appear to be "food poor" for juvenile cavefish. Food regimes change between post-larval and adult stages to become more dependent on partially decomposed material, guano, or detritus from the mud. We discuss the data with regards to our current developmental and genetic understanding of cavefish morphological and behavioural evolution, particularly regarding its enhanced Vibration Attraction Behaviour (VAB).

Towards an integrated approach to understand Mexican cavefish evolution

“…In the Chica cave, Bridges described large females with eggs and small specimens that he estimated to be less than a month old, as reported in [66]. The dry season was suggested to correspond to the cavefish breeding period, which is consistent with the report of juveniles in Pachó n in March 2016 [1]. If confirmed, this would suggest a 'synchronized' breeding season from South to North of the Sierra-different from the North America Amblyopsid cavefish, which breed after spring floods that introduce food into caves [74].…”

“…Nevertheless, examination of wild cavefish gut contents containing bat guano, mud, plankton, insects and congener fragments in different seasons suggested well-nourished adults with non-specialized dietary regime in the Chica, Sabinos, Subterráneo and Pachó n caves [1,66 -68]. Pachó n cavefish growth rate is comparable to their surface conspecifics [65] and healthy juveniles with digestive systems containing large numbers and varieties of micro-arthropods are found [1], suggesting excellent hunting skills in blind fry, like in laboratory conditions [69]. Subterráneo wild cavefish are more responsive to olfactory stimuli than eyed hybrids cohabiting in the cave [70], suggesting that olfactory skills described in the laboratory [29] are also at work in the natural environment.…”

Evolution of gastrointestinal tract morphology and plasticity in cave-adapted Mexican tetra, Astyanax mexicanus

“…A plausible explanation for this is differences in cave ecology. The Pachón cave is less impacted by seasonal flooding and has cave-adapted micro-crustaceans that could serve as a food source (15). Thus, our data suggest that specializations for individual caves may have occurred.…”

“…A. mexicanus is a species of small fish that exists as river-and cave-adapted populations that evolved on very different diets (15,16). The river (surface) fish have access to insects and plants in abundance, while in the cave, the absence of light makes cavefish dependent on bat droppings or material brought in by seasonal floods (15,16).…”

Utilizing the blind cavefish Astyanax mexicanus to understand the genetic basis of behavioral evolution

“…Cavefish from multiple populations exhibit this behavior, whereas few surface fish display VAB (Yoshizawa et al, 2010). Small invertebrates, which can serve as prey for these fish within their natural habitats (Espinasa et al, 2017), elicit vibrations of a frequency that elicit this behavior (Montgomery and Macdonald, 1987;Yoshizawa et al 2010), suggesting that VAB evolved to help cavefish find food in the dark. Indeed, this behavior is advantageous in cave-like conditions; fish with VAB are more successful at prey capture in the dark compared with fish without VAB (Yoshizawa et al, 2010).…”