Phenotype Linked Fertility Hypothesis, The
Male secondary sexual (attractiveness or competitive) characters signal male fertility to potential female mates.
The phenotype linked fertility hypothesis (PLFH) posits that male attractiveness traits, such as extravagant plumage, courtship, or weapon-like appendages, function as honest signals of male fertility. Robert Trivers (1972) reasoned that generally higher mating rates and the corresponding potential in males to become sperm depleted imposes selection on females to avoid sperm limited males. Males with the most vigorous courtship are indicating their sexual competence and adequate sperm supplies. Correspondingly, any physical trait that males possess enhancing the appearance of this vigor would be exposed to strong sexual selection and quickly exaggerated through mate choice. The PLFH has also been invoked as an explanation for the observation that many bird species, which tend to exhibit social monogamy, have offspring sired by males other than...