Table 1.

A review of evidence suggesting that males suffer a trade-off between expenditure on gaining matings versus expenditure on gaining fertilizations.

species	evidence	references
acanthocephalan worms	testes mass decreases with increasing sexual size dimorphism (a proxy for the intensity of male contest competition)	[143]
insects
Cyrtodiopsis dalmanni	juvenile hormone application increases eye span at the expense of testes mass	[144]
Onthophagus nigriventris	ablation of developing horns in pre-pupae increases testes mass in adults	[145]
Gnatocerus cornutus	selection for increased mandible size generates correlated reduction in testes mass	[146]
Teleogryllus oceanicus	negative genetic correlation between courtship song structure and ejaculate quality	[147]
Nauphoeta cinerea	competitive interactions between males decrease spermatophore size and sperm numbers	[148]
Panorpa cognate	negative genetic correlation between attractiveness and ejaculate investment per mating	[149]
Photinus greeni	negative phenotypic correlation between attractiveness and competitive fertilization success	[150]
Hemideina crassidens	males with large weapons have relatively smaller testes and ejaculate volumes than males with small weapons	[151]
amphibians
Crinia georgiana	negative among population covariation between testes mass and forearm development	[152]
fishes
Oncorhynchus kisutch	breeding coloration negatively correlated with sperm motility	[153]
Salvelinus alpinus	negative phenotypic correlation between red spawning coloration, dominance status and sperm density	[154,155]
Poecilia reticulata	negative genetic correlation between ornamentation and ejaculate quality	[156]
Pomatoschistus minutus	males lacking breeding coloration have testes 4.3 times larger, in absolute terms, than males with breeding coloration	[157]
Thalassoma bifasciatum	males with high mating success divert resources towards mate guarding at the expense of gamete production	[81]
birds
Chlamydotis undulata	males with exaggerated courtship displays show rapid deterioration in spermatogenic function compared with males with less elaborate displays	[158]
Gallus gallus domesticus	decline in ejaculate quality is associated with success in dominance interactions	[159]
Malurus melanocephalus	negative phenotypic correlation between plumage ornamentation and ejaculated sperm numbers	[160]
mammals
pinnipeds	among harem breeders, testis mass decreases with degree of sexual size dimorphism (a proxy for the intensity of male contest competition)	[161]
Homo sapiens	negative phenotypic correlation between voice attractiveness and ejaculated sperm numbers	[162]