Sperm precedence is the tendancy of a female who has bred with multiple males to give birth to the offspring of those males in unequal proportions. It thus only occurs in species breeding through sexual reproduction and with gametes of different sizes (anisogamy), which the majority of sexually reproducing species have.
Not all sexually reproducing species with anisogamy exhibit multiple mating by males with each reproductive female, so it has not been identified in all sexually reproducing species. Nevertheless, anisogamy leads to sperm competition, an aspect of sexual selection, so sperm precedence is an important factor in the occurence of sperm competition in species with such behaviour.
Sperm competition occurs in sexually reproducing species that have unequally sized gametes, that is they exhibit anisogamy. But why should gametes be of different sizes?
There have been a number of suggestions of why this occurs in many species, but one relates to the advantage that a sex producing smaller microgamates (sperm) has in attempts at fertilisation of macrogametes (ova). Because macrogametes are much more costly to produce the sex producing them cannot keep up with the number of microgametes produced by the other sex.
Thus if selection starts on the gametes of one sex in a sexually reproducing species with equally sized gametes (isogamy), selection towards smaller gametes is likely to be successful.[1] This cannot continue indefinitely, because microgametes must carry the genetic material of one sex, and must contain organelles to make them motile towards macrogames and to enable them to fuse with a macrogamete to form a zygote.
What is sperm competition?
In anisogamous species, because one sex produces many more microgametes than the other does macrogametes, microgametes (sperm) compete with each other for successful fertisation of each ova.[a] This occurs irrespective of the mating behaviour of the males producing the sperm.
However where male-female mating behaviour involves competition by males for access to females, then sperm competition can become more complex.[2]
When does sperm precedence occur?
Sperm precedence requires the same conditions as sperm competition. But it cannot be identified in all species where sperm competition has been identified, because it requires example species where:
Females normally mate with multiple males.
It is ethically sound to investigate the progress of sperm from multiple males in fertilising each female.
It is ethically sound to reproduce this investigation across replicates of females.
It is thus not surpring that sperm precedence has been identified in less groups of organisms, typically invertebrates, than sperm competition. (See Table 6.2[2]:128 for examples of taxa where sperm competition has been identified.) Nevertheless, if these conditions can be satisfied, then sperm precedence can be investigated.
Examples of sperm precedence
Sperm precedence has been identified in diverse groups of animals where females mate with multiple males. Examples are given in the table below. It is not surprising that many are found in insects, the most diverse group of Arthropoda and far more diverse (that is, including far more species) than the whole of vertebrates, the group containing mammals. Another group where examples are found are arachnids, including many spiders.
The only vertebrate and mammalian example is the house mouse because it has been bred for experimental work (the laboratory mouse) and thus can satisfy ethical requirements for lab work on vertebrates.[3]
The most frequently found types of sperm precendence are temporal, that is relating to the order in which a male mates with a female in a sequence of matings. If the first male to mate is likely to have an advantage, then sperm precendence is described as first male precedence. If the last male to mate is likely to have an advantage, then sperm precendence is described as last male precedence.
Other types of sperm precedence have been suggested. Sperm precedence can favor the male whose sperm are the most motile, or the male whose sperm were delivered closest to the female's ova.
The species where sperm precedence has been identified in the table shown in Examples of sperm precedence above give indication of where the different types of sperm precedence occur.
Species exhibiting different types of sperm precedence
Many insects exhibit last male precendence. This includes Anthidium manicatum the European wool carder bee, although the authors of the research on this species also write: "Or at least 'late' male precedence".[5]:211 This suggests some change in advantage in the sperm precedence of later males.
Of those insect species given in the table above the two ladybird beetle species Eriopis connexa[8] and Harmonia axyridis[9] are the exceptions. Eriopis connexa is included because it is a species where males and females mate multiple times with each other and the reference provided was a search for sperm precendence.[8] However, no consistent trend for sperm precendence was found. Harmonia axyridis, in contrast to most other insect species, exhibits first male precendence.
The two spider species given, also invertbrates, but part of Arachnida rather than Arthropoda the group to which insects belong, both exhibit first male precedence.[15][16]
The house mouse example is unusual. The only reason it can be included is that it has been bred for laboratory work and thus satisfies ethical standards. Researchers in the study given suggested that last male precedence could be found in breeding among certain haplotypes distinct from the wildtype.[3]
Explaining sperm precedence
As mentioned above, many insects exhibit last male precedence. But one of the insect species considered here exhibits firat male precedence.
Either of these phenomena may be a consequence of the reproductive anatomy of insects. Female insects (and females of some other groups) have spermathecae, organs that can receive and store sperm from males following mating. Thus, the existence of spermathecae means that sperm do not travel directly to ova during reproduction and sperm competition between early- or late-mating males may be controlled by female behaviour.[citation needed]
This does not provide an evolutionary answer for the occurence of sperm precedence, nor does it provide an explanation for the occurence of sperm precedence in animal groups that do not have spermathecae. Other answers are needed for these questions.[citation needed]
Notes
↑The term ova is used here rather than egg because egg has multiple usages.
↑Parker, G A; Baker, R R; Smith, V G F (1972). "The origin and evolution of gamete dimorphism and the male-female phenomenon". Journal of Theoretical Biology. 36 (3): 529–553. doi:10.1016/0022-5193(72)90007-0. PMID5080448.
↑Kock, Dagmar; Sauer, Klaus P. (2007). "High variation in sperm precedence and last male advantage in the scorpionfly Panorpa germanica L. (Mecoptera, Panorpidae): Possible causes and consequences". Journal of Insect Physiology. 53 (11): 1145–1150. doi:10.1016/j.jinsphys.2007.06.002. PMID17632122.
12Lampert, Kathrin P.; Pasternak, Vanessa; Brand, Philipp; Tollrian, Ralph; Leese, Florian; Eltz, Thomas (2014). "'Late' male sperm precedence in polyandrous wool-carder bees and the evolution of male resource defence in Hymenoptera". Animal Behaviour. 90: 211–217. doi:10.1016/j.anbehav.2014.01.034.
↑Drnevich, Jenny M. (2003). "Number of mating males and mating interval affect last-male sperm precedence in Tenebrio molitor L". Animal Behaviour. 66 (2): 349–357. doi:10.1006/anbe.2003.2219.
↑Eady, Paul E.; Rugman-Jones, Paul; Brown, Denise V. (2004). "Prior oviposition, female receptivity and last-male sperm precedence in the cosmopolitan pest Callosobruchus maculatus (Coleoptera: Bruchidae)". Animal Behaviour. 67 (3): 559–565. doi:10.1016/j.anbehav.2003.07.003.
123Silva, Alessandra C.G.; Silva-Torres, Christian S.A.; Nascimento, Deividy V.; Torres, Jorge B. (2021). "Sexual maturity, lack of partner choice and sperm precedence in the promiscuous ladybird beetle Eriopis connexa (Germar): Who is my father?". Behavioural Processes. 192 104500. doi:10.1016/j.beproc.2021.104500. PMID34509563.
↑Franck, Pierre; Solignac, Michel; Vautrin, Dominique; Cornuet, Jean-Marie; Koeniger, Gudrun; Koeniger, Nikolaus (2002). "Sperm competition and last-male precedence in the honeybee". Animal Behaviour. 64 (3): 503–509. doi:10.1006/anbe.2002.3078.
↑Xu, Jin; Wang, Qiao (2010). "Thiotepa, a reliable marker for sperm precedence measurement in a polyandrous moth". Journal of Insect Physiology. 56 (1): 102–106. doi:10.1016/j.jinsphys.2009.09.009. PMID19799908.
↑Otronen, Merja (1997). "Variation in sperm precedence during mating in male flies, Dryomyza anilis". Animal Behaviour. 53 (6): 1233–1240. doi:10.1006/anbe.1996.0425. PMID9236019.
↑Haubruge, Eric; Arnaud, Ludovic; Mignon, Jacques (1997). "The Impact of Sperm Precedence in Malathion Resistance Transmission in Populations of the Red Flour Beetle Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)". Journal of Stored Product Research. 33 (2): 143–146. doi:10.1016/S0022-474X(96)00045-8. hdl:2268/26120.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
