The unexpected consequences of intercourse with an old lady (beetle)

Recently, I posted about one of my favorite symbiont-host systems: mites that are sexually transmitted among their lady beetle hosts. Because that system is so empirically tractable, studies on mites and lady beetles are increasing our understanding of STIs by leaps and bounds. Today I want to talk about another really cool thing that we just learned by studying lady beetle sex.

In order for symbionts to be maintained in host populations over the long term, there needs to be transmission of the symbiont from one host generation to the next. In temperate regions, many animals have seasonal population cycles where adults from multiple generations don’t overlap and/or adults and their offspring don’t temporally overlap. For instance, many dragonflies lay eggs in the summer/fall and then die. The eggs hatch into aquatic larvae, which then overwinter and don’t emerge until the next year. In that case, adult dragonflies from the first generation never see the adult dragonflies from the second generation, so those dragonflies wouldn’t be able to pass on STIs between generations.

Coccipolipus hippodamiae lady beetles overwinter as adults, not larvae. They emerge in the spring, and in May-June they have lots of sex and lay lots of eggs. Eventually, the overwintered adults die. Also, at some point, the new cohort emerges from the eggs and individuals develop from larvae to sexually mature adults.

Interestingly, not all Coccipolipus hippodamiae lady beetle populations have mites, and the presence or absence of mites in a population is consistent over time (Pastok et al. 2015). Populations north of 61°N tend to be mite-free, and populations south of 61°N tend to have mites. But lady beetles in populations north of 61°N can become infected by mites and transmit them in the laboratory, so it doesn’t seem like there is a physiological/biological reason why northern and southern populations differ in mite infection (Pastok et al. 2015).

Instead, that division by latitude suggests that ecology (specifically, phenology) might play an important role in intergenerational mite transmission. And sure enough, in August, southern mite populations have adults from both the overwintered lady beetle generation and the new lady beetle generation (Pastok et al. 2015). And at least some of the new adults have already had sex when the old generation is still present, which means that sexual contacts could be happening between the generations. In contrast, in the northern populations, the overwintered lady beetles die sooner and the new lady beetles mature later, so there is no overlap among generations (Pastok et al. 2015). It looks like that generation gap prevents sexually transmitted mites from persisting in those northern populations! SO. COOL.

So, phenology plays a really important role in symbiont transmission when symbionts are sexually transmitted. But that’s not all! For instance, symbionts that require multiple host species may also be very sensitive to host phenology, especially when there are mismatches in the phenologies of various host species (here and here). As host phenologies continue to change in response to the changing global climate, the role of host phenology in symbiont transmission will remain a huge area for future research.

sexwitholdladies

Reference:

Pastok, D, M-J Hoare, J.J. Ryder, M. Boots, R.J. Knell, D. Atkinson, and D.D. Hurst. 2015. The role of host phenology in determining the incidence of an insect sexually transmitted infection. Oikos.

Insect STDs

Happy Valentine’s Day, Everyone!!

Speaking of romance…

A while back, I posted about the difference between density-dependent and frequency-dependent disease transmission.  The “typical” example of a parasite/pathogen with frequency-dependent transmission is one that is sexually transmitted.

For humans and other mammals, most STDs are caused by viruses or bacteria (e.g., HIV, gonorrhea, chlamydia).  One notable exception is pubic lice.  However, for things like insects, all kinds of parasite taxa can be sexually transmitted.  In fact, most insect STDs are from multicellular parasites!  Sexual transmission is an especially successful strategy when host organisms are mostly solitary, so that interactions are rare outside of the breeding season.

There’s a link below to a review with all kinds of insect STD info – check it out!

insectsexed

Don’t judge.  The world needed this.

Reference:

Knell, R.J., and K.M. Webberly.  2004. Sexually transmitted diseases of insects: distribution, evolution, ecology and host behaviour.  Biol Rev 79(3): 557-81.  (Direct link to PDF download)

Rove Beetles Eat Parasites (mind=blown)!

I found a big rove beetle in my yard today, and I decided to take some photos of its giant mandibles.  It was behaving oddly – maybe just because it didn’t like my attentions, or maybe because it was parasitized.  I decided to do some research into rove beetle parasites, and I discovered something tangential that blew my mind: rove beetles eat parasites!!

As I might have mentioned before, I’m really interested in predation on parasites, and I have a special soft spot for mutualistic organisms that eat parasites.  It turns out that there is a whole group of rove beetles (Amblyopinus) that live on rodents and in their nests.  These beetles were originally classified as parasites of rodents, but Ashe and Timm (1987) argued that they didn’t appear to be parasitic; rodents did not try to groom off their rove beetles, and beetles were never seen damaging host tissues.  Instead, Ashe and Timm (1987) found that the rove beetles hang out in the rodents’ nests during the day, eating ectoparasites, and hang out on the rodents at night so that they get free transportation among nests.  AWESOME!

I think that this is the first time I’ve heard of multicellular symbionts of mammals that eat parasites.  Can you think of any others? Remoras on cetaceans?

Relevant.

Reference:

Ashe, J.S., and R.M. Timm. 1987. Probable mutualistic association between staphylinid beetles (Amblyopinus) and their rodent hosts.  Journal of Tropical Ecology, 3(2): 177-181.

Lady Beetles and Parasites as “Weapons”

Everyone knows that lady beetles are awesome.  But if you have somehow missed out on the lady beetle fan club until now, here’s your chance to get in on the lady beetle love.  Asian lady beetles use “biological weapons” – parasite weapons [Relevant]  This is awesome enough that it made it into the May issue of Science.  The story goes like this:

Asian lady beetles, aka Harlequin lady beetles, are the ones that you see all the time.  They’re not native; we introduced them to control our agricultural pests.  The problem is that the Asian lady beetle then turned into a pest, mostly because the arrival of this species caused declines in populations of native species of lady beetle.  That’s sad, because there are some really, really cool lady beetles out there, and we don’t want them to go away.

What is it about these Asian lady beetles that causes the declines in the native species?  One reason is that ALBs have symbiotic fungi.  These are actually microspordian parasites, but it turns out that ALBs aren’t affected by the parasites (probably because ALBs have tons of antimicrobial peptides).  However, the parasites are quite deadly to other, native lady beetle species.     

If science doesn’t work out, I think I’ve got a career in lady beetle art?

How do the ALBs use their killer fungi on native species?  BAZOOKAS.  Ok, not really.  It turns out that these fungi end up in the ALB eggs, and it just so happens that lady beetles tend to eat the eggs of competing species.  So, a native lady beetle comes along, tries to wipe out some future ALB babies while simultaneously having an afternoon snack, and ends up getting infected by the fungus.  Awe-some.  Well, ok, not awesome, but you gotta hand it to the ALBs and their parasites.

Should we try taking antimicrobial peptides from ALBs and injecting them into native lady beetle species?  

Reference:

Vilcinskas, A., K. Stoecker, H. Schmidtberg, C. Rohrich, and H. Vogel. 2013. Invasive Harlequin ladybird carries biological weapons against native predators. Science 340(6134): 862-863.

Zombie Ants

Instead of talking about a specific paper today, I’m going to talk about ZOMBIE ANTS <cue horror music>.  Parts of this will count as self-plagiarism, because I’ve blogged about this in other places.  Let the post cannibalism begin!

I attended the annual meeting of the American Society of Parasitologists last summer, and it was awesome.  David Hughes gave a really awesome talk called “Zombie Ants: The Precise Manipulation of Social Insect Behavior by a Fungal Parasite.”  I’m sure you’re totally hooked already, but just in case you’re not seeing how cool this is, let me reel you in with some photos.  (These aren’t ants, but you’ll see those later.)

Photo from here.

Photo from here.   For more cool fungus pics, just google “Cordyceps fungus.”

Parasites often manipulate their host’s behavior in order to increase the probability that they (the parasites) will be successfully transmitted to their next host.  In the case of the parasitic fungus of these ants, the fungus wants the ant to go hang out somewhere that will result in the fungus being able to rain spores down on other ants.  It does this by making the ants climb up to a leaf above an area of a high ant traffic (areas that Hughes calls “killing fields”). The ant is then “forced” to bite down on the main vein of that leaf, and then its mandibles get stuck that way, so that the ant is attached to the underside of the leaf forever.  Then the fungus sprouts out of the ant’s head and does its whole raining spores of death thing.

Since David Attenborough explains things better than I do, I’m going to link you to David Hughes’ website, where he has more info and some sexy videos (including Attenborough).

As a final note, Hughes is looking into using this parasitic fungus as a form of biocontrol for pest ants, like on farms.  In other words, YOU TOO could have your very own ZOMBIE ANTS.

How do you feel about using parasites as biocontrols?  That’s a huge can of worms, I know, but I’d like to hear your opinions.