Alternative reproductive tactics

taktyki rozrodcze

Spring in our climate zone is the time of reproduction for most organisms, but it is not uniform in all of them. Some animal species, both vertebrate and invertebrate, adopt diverse reproductive tactics. Diverse within one, and the same species, we add. Tactics and strategy are terms mainly used in the art of war. But in love, as in war, that’s why behavioral ecologists have adapted this military nomenclature to describe alternative reproduction tactics( ART) found in one species. This interesting phenomenon also occurs in fish!

What are alternative reproductive tactics?

Alternative reproductive tactics take many forms. They often involve two categories of males: guardians or caretakers ( guarders/ parents) and sneakers, cuckolds. The guards compete for mates, build nests, and often guard eggs and young. Sneakers, on the other hand, avoid violence, copulate secretly, sometimes posing as females, sexually immature juveniles or individuals of another species to trick their chances of reproduction.

Several types of reproductive migrations are also observed, such as in dioecious fish. After spawning, some individuals remain in freshwater or physiologically die of old age, and some steam back up rivers, dying only due to predation or accident, for example: in sturgeon. A prerequisite for the fulfillment of the definition remains the discrete (jumping, very pronounced) rather than continuous nature of differences between alternative versions of individuals of one species. This ontological divide is revealed at the level of genes as well as appearance and behavior [3, 7].

You praise what you don’t know

In behavioral ecology classes, alternative reproductive techniques are usually given little time, usually illustrated with examples from birds, mammals, and possibly arthropods. And yet the world of fish is just as fascinating! It is not at all necessary to look for them in the depths of the seas, among the corals of the Great Reef or in the waters of the Amazon. Alternative reproductive tactics are practiced by males of the native salmonids Salmonidae, Pontocaspian gobies Gobidae or Rhodeus sericeus.

In Polish textbooks of ichthyology and sozology, and even more so in albums for anglers, there is no mention of the occurrence of ART in native salmonids: sea trout Salmo trutta morpha trutta and Atlantic (noble) salmon Salmo salar. From the salmon chapter GIOŚ methodological manual [5] we learn about two alleged subpopulations: summer and winter, and about spawning occurring in Poland from October to December (at 5-6°C heat, in sections of rivers with gravelly bottoms), but not a word about the fact that some males do not swim to the seas at all or undergo metamorphosis (smoltification). The life cycle of salmon is often presented as follows: roe> alevin> parr>smolt -> sexually mature individual (spawner).

Meanwhile, not only in Pacific salmon Oncorhynchus sp. div. but also in our own S. salar, some males pretend to stall in development. They still look like parries, still remain in freshwater, relatively close to their hatching sites, and yet become fully sexually mature. Instead of floating down rivers, feeding for years in the sea or some huge lake, and then laboriously swimming upstream and preparing their nests, they wait for the females on the spot [3]. Some sea trout behave similarly, although they trumpet later than salmon, as from December to April [1].

The largest family of the smallest fish

Gobidae is the most species-rich family of marine fishes, with only a few representatives in (say) fresh waters. Among its tropical members we find several candidates for the status of the world’s smallest fish and smallest vertebrate in general. In the vast majority of gobies, the eggs laid near the bottom are guarded by the male. And where there are nests, there are often alternative reproductive strategies. The plantains that are settled with us are no exception. For example, two morphs of males have been recorded in the Lower Rhineland gobies (bullheads) Neogobius melanostomus, which pursue two reproductive tactics. Smaller males (9.85 cm and above) are stealthy, while their larger brothers are good fathers/caregivers of children [2].

A couple of months ago, the presence of two types of males was shown in 3 species of gobies (including again for the b. breakfasttail) in their original homeland, in the rivers of Iran. Males are either large warriors maturing in late adolescence, with dark coloring and wide chada jaws, making elaborate courtships and fighting with rivals, or small cuckolded males maturing in youth, with light coloring and narrow jaws, not adoring females or fighting with males of the first type [9].

Until now, the successes of gobies have been explained by their origin in the Pontocaspian region. There, they have adapted to changes in salinity, smothering, naturally high concentrations of heavy metals, foraging for crayfish and other such hindrances. Art. may give gobies an added advantage over other fish. Even if the new environment turns out to be absolutely unfriendly to one morph, alternative tactics here may have an advantage over the native fauna and cope with the climate [4].

A living incubator

Common pinks (hatchetfish) Rhodeus sericeus are the only ostracophiles, or fish that spawn into mollusk shells, in the European fauna. Little! Unlike the cichlids we’re familiar with from aquariums, these adorable cyprinids lay their eggs and then their milt into the gill lobes of a live scaphopod clam, rather than into an empty shell. A mister-ink treats a scurvy or bristlefish similarly to how a mister-ink or mister-ink treats its nest. He therefore guards it from other males, while showing it off to females. And where the males guard the nests, there also appear creeps secretly flooding the eggs with their sperm. Across the board, Rosewood is no exception in this regard. In her case, too, the masters are divided into caretakers and kukolds, although their house is alive.

The Common Rose proved to be unique in another respect. Namely, it is the only species known so far in which the Coolidge effect (an increase in libido after changing partners, typical of chickens, rats and humans, among others) operates at a level other than inside the female’s body, and the only example of this effect in an organism with external fertilization. Gentlemen’s libido increases after the change of incubator. A live scorpionfish or rattlesnake is therefore a direct analogue of the female reproductive system of species with internal fertilization [6].

Three sources of thousands of tactics

The diversity of reproductive modes in bony fishes remains an evolutionary mystery. Among Teleostea , we will meet all types of reproduction observed in vertebrates, but also a few peculiar ones. The number is increased by alternative reproductive tactics. The reasons for the diversity are probably the duplication of the entire genome, the way the gonads differentiate, and the organization of the brain-pituitary axis [7]. Genome duplication duplicates the pool of available genes. In turn, this increases the rate of evolution, including the evolution of reproductive behavior.

Fish gonads are formed from somatic mesoderm cells, so – regardless of the method of sex determination (environmental or genetic) – fish retain their protogenic potential. That’s why there are so many hermaphrodites among them, as well as species that change sex with age or as life requires. This labile nature of the gonads also means that males of one species can mature in very different ways (at different ages, in different environments) and then pursue a range of alternative reproductive tactics.

In skeletons, the nervous and endocrine systems are more adaptive than in other vertebrates. Their pituitary gland works differently, more precisely, integrating the two systems so strongly that you can basically talk about one – the neuroendocrine system. As a result, they respond to environmental and social challenges (of their own population) in a variety of ways not available to the rest of the mandibles [8].

Seek and you shall find. However, you must have the right tools for your search!

The example of alternative reproductive tactics shows the importance of inquisitiveness and language skills. Polish professional and popular literature lacks any mention of ART in the native and permanently established fishes of Poland. Meanwhile, the noble salmon provides a pretty good example of this tactic. It is noteworthy that being its opposite in many respects (native, size, resistance to climate change and water pollution…) gobies acutely behave very similarly in the field of reproductive tactics. And just as with salmon, the issue of ART remains overlooked in domestic science and popularization. In contrast, the roseate – with its Coolidge effect on external fertilization – has proven to be as unique in terms of ART as it is in terms of its choice of egg-laying sites.


Photo. main: By Ostjan, CC BY-SA 3.0/Wikipedia

In the article, I used, among other things. From the works:

  1. Birnie-Gauvin K., Thorstad E.B., Aarestrup K. (2019). Overlooked aspects of the Salmo salar and Salmo trutta lifecycles. Reviews in Fish Biology and Fisheries, 29(4), 749-766.
  2. Bleeker K., De Jong K., Van Kessel N., Hinde C.A., Nagelkerke L.A. (2017). Evidence for ontogenetically and morphologically distinct alternative reproductive tactics in the invasive Round Goby Neogobius melanostomus. PLoS One, 12(4), e0174828.
  3. Helfman G., Collette B., Facey D., Bowen B. (2009). The Diversity of Fishes: Biology, Evolution, and Ecology. Wiley & Blackwell, West Sussex (UK) – New York (US).
  4. McCallum E.S., Bose A.P., Lobban N., Marentette J.R., Pettitt-Wade H., Koops M.A., … Balshine S. (2019). Alternative reproductive tactics, an overlooked source of life history variation in the invasive round goby. Canadian Journal of Fisheries and Aquatic Sciences, 76(9), 1562-1570.
  5. Sobieszczyk P. (ed.) (2012). 1106. Atlantic salmon Salmo salar. Ss. 248-263. In: Makomaska-Juchiewcz M., Baran P. (eds.) Monitoring of animal species – Volume III. GIOŚ, Warsaw.
  6. Spence R., Reichard M., Smith C. (2013) Strategic sperm allocation and a Coolidge effect in an externally fertilizing species. Behavioral Ecology 24, 82-88.
  7. Taborsky M., Oliveira R.F., Brockmann H.J. (2008). The evolution of alternative reproductive tactics: concepts and questions. Alternative reproductive tactics: an integrative approach, 1: 21.
  8. Wotton R.J., Smith C. (2015). Reproductive Biology of Teleost Fishes. Blackwell-Wiley, Oxford.
  9. Zarini S., Poli F., Balshine S. (2023). Alternative reproductive tactics in goby fishes of the Caspian Sea. Journal of Fish Biology, 103(6), 1252-1263.

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