100% of female Globodera pallida nematodes are polyandrous

In a recent study published in the journal Ecology and Evolution, a group of NEM-EMERGE partners from INRAE and ANSES have confirmed for the first time that polyandry occurs within the potato cyst nematode Globodera pallida. Although multiple paternity is a common reproductive behaviour in nature, this has never been demonstrated and quantified for this species.
By genotyping Globodera pallida juveniles from the same cyst using microsatellite markers, this work demonstrated multiple paternity in this species and showed that 100% of females were polyandrous, “with an average of 7 fathering males”, stated researchers.

Moreover, “and contrary to our expectations, the mating rate with different males appeared to
remain stable during the adaptation process to a masculinizing potato resistance”. The most frequently used resistant potato cultivars, derived from the wild species Solanum vernei, act by masculinizing nematode populations. The mechanism of sex determination of potato cyst nematodes is driven by the quality of the syncytium (the feeding site they form in their hosts) and the availability of nutrients, with juveniles moulting into adult females when nutrient levels are high and into males when nutrients are lower. When juveniles reach the roots of resistant cultivars, they fail to elicit the formation of a functional syncytium, and therefore, they are unable to develop into females.

However, the intensive deployment of this resistance has led to the emergence of virulent populations that can overcome the resistance. The proportion of adult males in the virulent populations consequently varies over time during the adaptation process, with a decreasing proportion of males. This fact led the authors to expect lower frequencies of polyandry in virulent populations, given that in many species polyandry is more frequent in male-skewed populations. Results didn’t confirm this, though, as they found genetic evidence of multiple paternity within all the cysts analysed.

According to researchers, the level of polyandry may represent an important parameter to integrate into demogenetic models designed to explore the nematode’s adaptation to potato resistance.