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Many parasites can interfere with their host’s defences to maximize their fitness. Here we investigated if there is heritable variation in the spider mite, Tetranychus evansi for traits associated with how they interact with their host plant. We also determined if this variation correlates with mite fecundity. This mite has the ability to interfere with jasmonate (JA) defences which is the main determinant of anti-herbivore immunity in plants. We investigated (i). variation in fecundity in the presence and absence of JA defences, making use of a wild-type tomato cultivar and a JA-deficient mutant (defenseless-1), and (ii) variation in the induction of JA defences, in 4 T. evansi field populations and in 59 inbred lines created from an outbred population conceived from controlled crosses of the four field populations. We observed a strong positive genetic correlation between fecundity in the presence (on WT) and in the absence of JA-defenses (on def-1). However, fecundity did not correlate with the magnitude of induced JA-defenses in WT plants. Our results suggest that JA-defences have a minimal impact on the performance of the specialist T. evansi, either because all lines can adequately reduce levels of defences, or because they are resistant to such defences.

Laboratory studies are often criticized for not being representative of processes occurring in natural populations. This can be partially mitigated by using lab populations that capture large amounts of variation. Additionally, many studies addressing adaptation of organisms to their environment are done with laboratory populations, using quantitative genetics or experimental evolution methodologies. Such studies rely on populations that are either highly outbred or inbred. However, the methodology underlying the generation of such biological resources are usually not explicitly documented.Given their small size, short generation time, amenability to laboratory experimentation and knowledge of their ecological interactions, haplodiploid spider mites are becoming a widely used model organism. Here, we describe the creation of outbred populations of two species of spider mites, Tetranychus urticae and T. evansi, obtained by performing controlled crosses between individuals from field-collected populations. Subsequently, from the outbred population of T. evansi, we derived inbred lines, by performing several generations of sibmating. These can be used to measure broad-sense heritability as well as correlations among traits. Finally, we outline an experimental evolution protocol that can be widely used in other systems. Sharing these biological resources with other laboratories and combining them with the available powerful genetic tools for T. urticae (and other species) will allow consistent and comparable studies that greatly contribute to our understanding of ecological and evolutionary processes. DPG and SM designed the study with help from LRR and FZ. DPG and LRR collected the spider mite populations. The creation of the outbred and inbred populations was performed by DPG, MAC, MCM, JTP and CE. FZ and IF developed the formula to calculate the coefficient of inbreeding and the effective number of generations of selection. The manuscript was written by DPG and SM with considerable contributions from all authors. References Agashe, D. (2009). The stabilizing effect of intraspecific genetic variation on population dynamics in novel and ancestral habitats.

Many parasites can interfere with their host's defences to maximize their fitness. Here, we investigated if there is heritable variation in the spider mite Tetranychus evansi for traits associated with how they interact with their host plant. We also determined if this variation correlates with mite fecundity. Tetranychus evansi can interfere with jasmonate (JA) defences which are the main determinant of anti-herbivore immunity in plants. We investigated (i) variation in fecundity in the presence and absence of JA defences, making use of a wild-type tomato cultivar and a JA-deficient mutant ( defenseless-1 ), and (ii) variation in the induction of JA defences, in four T. evansi field populations and 59 inbred lines created from an outbred population originating from controlled crosses of the four field populations. We observed a strong positive genetic correlation between fecundity in the presence (on wild-type) and the absence of JA defences (on defenseless-1 ). However, fecundity did not correlate with the magnitude of induced JA defences in wild-type plants. Our results suggest that the performance of the specialist T. evansi is not related to their ability to manipulate plant defences, either because all lines can adequately reduce levels of defences, or because they are resistant to them.