Reproduction and the Early Development of Vertebrates in Space: Problems, Results, Opportunities

Abstract

Humans and animals adapt to space flight conditions. However, the adaptive changes of fully formed organisms differ radically from the responses of vertebrate embryos, foetuses, and larvae to space flight. Development is associated with active cell proliferation and the formation of organs and systems. The instability of these processes is well known. Over 20 years has passed since the last systematic experiments on vertebrate reproduction and development in space flight. At the same time, programs are being prepared for the exploration of Mars and the Moon, which justifies further investigations into space flight's impact on vertebrate development. This review focuses on various aspects of reproduction and early development of vertebrates in space flights. The results of various experiments on fishes, amphibians, reptiles, birds and mammals are described. The experiments in which our team took part and ontogeny of the vertebrate nervous and special sensory systems are considered in more detail. Possible causes of morphological changes are also discussed. Research on evolutionarily and taxonomically different models can advance the understanding of reproduction in microgravity. Reptiles, in particular, geckos, due to their special features, can be a promising object of space developmental biology.

Keywords: amphibians; birds; development; fishes; mammals; microgravity; nervous system; reproduction; reptiles; space flight; vertebrates.

Figure 1

Microphotographs of horizontal sections through the head of Xenopus laevis tadpoles, hematoxilin and eosin. (a) Flight group (b) Control group. 1—olfactory placode, 2—oral cavity, 3—eye, 4—brain anlage, 5—otic vesicle.

Figure 2

(a) Unfertilized egg of thick-toed gecko laid by a female on the wall of a flight container (Foton-M3, 12 days flight, 2007). (b) Male ornate day gecko before the flight experiment onboard unmanned spacecraft Foton-M4 (44.5 day flight, 2014).

Figure 3

Video capture of ornate day geckos, sexual behavior in weightlessness: mounting of a male on a female, seventh day of the flight (Foton-M4, 2014). 1—Feed box; 2—water bowl; 3—heating zones; 4—tubular shelters for geckos made of American oak; 5—research and support block (RSB) walls lined with American oak; 6—vents for ventilation and waste collection; 7—RSB floor made of textile laminate (a fabric reinforced laminate); 8—O₂/CO₂, temperature and humidity sensors; 9—cuttlefish shell as an additional source of calcium. Video camera and a fan are located on the ceiling of the container out of sight.

Figure 4

Veiled chameleon: late embryo before hatching (a), newborn cub (b). The photographs were taken in preparation for an unrealized experiment on the development of chameleons in space flight (own data). The scale bar is the same in both images, the smallest division is 0.5 mm.

Figure 5

Horizontal section through the head of Rattus norvegicus newborn pups (flight group (NIHR1). Mallory staining. Foci of degeneration (red arrows) are shown at low (a) and a higher (b–d) magnification; the rectangular on A highlights the region shown on (b–d). 1—Nasal cavity, 2—olfactory nerve, 3—olfactory bulb, 4—eye, 5—cortex telencephali, 6—hippocampus, 7—fourth ventricle, 8—cerebellum.