Experimental evolution of parasitic host manipulation

Abstract

Host manipulation is a parasite-induced alteration of a host's phenotype that increases parasite fitness. However, if genetically encoded in the parasite, it should be under selection in the parasite. Such host manipulation has often been assumed to be energetically costly, which should restrict its evolution. Evidence of such costs, however, remains elusive. The trophically transmitted cestode Schistocephalus solidus manipulates the activity of its first intermediate copepod host to reduce its predation susceptibility before the parasite is ready for transmission. Thereafter, S. solidus increases host activity to facilitate transmission to its subsequent fish host. I selected S. solidus for or against host manipulation over three generations to investigate the evolvability of manipulation and identify potential trade-offs. Host manipulation responded to selection, confirming that this trait is heritable in the parasite and hence can present an extended phenotype. Changes in host manipulation were not restrained by any obvious costs.

Behavior out of control: Experimental evolution of resistance to host manipulation

“…By contrast, host manipulation changed within a few generation in a similar experiment in which only the parasite was under selection (Hafer-Hahmann, 2019). By contrast, host manipulation changed within a few generation in a similar experiment in which only the parasite was under selection (Hafer-Hahmann, 2019).…”

“…In order to avoid being attacked by the perceived predator, copepods should reduce their activity following this "attack" (Benesh, 2010a;Hafer & Benesh, 2015;Hafer & Milinski, 2015, 2016Hammerschmidt et al, 2009). Changes in host activity over time ( at: https ://github.com/ferha h/copep odtra cking ) that automatically recorded copepod position (Hafer, 2018;Hafer-Hahmann, 2019). The copepod behavior was recorded for 15 min starting just before the drop with a HD-camera (MHD-13MG6SH-D, Mintron, Taiwan).…”

“…In the initial generation, copepods were distributed to selection line based on the extent of this host manipulation and then either selected for increased (susceptible) or decreased (resistant) host manipulation. Selected copepods were combined with (unselected) females from the same replicate to breed the next generation ( at: https ://github.com/ferha h/copep odtra cking ) that automatically recorded copepod position (Hafer, 2018;Hafer-Hahmann, 2019). To exclude random noise, a copepod was only considered moving if it moved by at least 5 pixel (about one copepod length).…”

“…I used a similar approach and design used recently to investigate the evolvability of host manipulation in S. solidus (Hafer-Hahmann, 2019). I used a similar approach and design used recently to investigate the evolvability of host manipulation in S. solidus (Hafer-Hahmann, 2019).…”

“…To better understand how readily resistance to host manipulation evolves, I experimentally selected the copepod Macrocyclops albidus for resistance or susceptibility to host manipulation by the cestode Schistocephalus solidus. I used a similar approach and design used recently to investigate the evolvability of host manipulation in S. solidus (Hafer-Hahmann, 2019). Schistocephalus solidus is well known to manipulate its first intermediate copepod host to modify its predation susceptibility according to its need; before the parasite becomes infective to its subsequent fish host, it reduces host activity (Benesh, 2010a;Hafer, 2018;Hafer & Benesh, 2015;Hafer & Milinski, 2015;Hammerschmidt et al, 2009) and predation susceptibility (Weinreich et al, 2013).…”