Sex: Not all that it’s cracked up to be?

While sexual reproduction is generally thought to be, evolutionarily speaking, a good idea, there are a small number of organisms that are testament to the contrary. The root-knot nematodes Meloidogyne incognita, M. javanica, and M. arenaria reproduce clonally using mitotic parthenogenesis but have a broader host range, a wider geographical distribution, and a greater agricultural impact than their sexual relatives (Fig 1) [1]. Remarkably, some of these species even have the ability to overcome host resistance [2], suggesting a mechanism for adaptation in the absence of sex. The genetic basis of this plasticity, both in terms of host range and adaptability, is not fully understood. Previous genome sequencing of Meloidogyne has shown that the genome of one of these species, M. incognita, is polyploid [3], most likely as a result of hybridisation (allopolyploid), with a further study suggesting that M. incognita may be the result of multiple additive hybridisation events: a hybrid of a hybrid [4]. To understand the impact of allopolyploidy on plasticity, Blanc-Mathieu et al. [5] resequenced the M. incognota genome and transcriptome (4 life stages) and sequenced the genomes of 2 related mitotic parthenogens, M. javanica and M. arenaria. These data were compared to existing assemblies of the meiotic parthenogen M. floridensis and the facultative sexually reproducing M. hapla.