The Pros and Cons of Mating with an Amazonian Female

By Rachel Wilson

Sex is important, and not just because it produces babies and facilitates social bonding but because it allows for genetic recombination. This allows offspring to be genetically unique which ultimately increases resilience of the species. In turn resilience increases the chances that at least some individuals in a population will be able to cope and adapt to random change in the environment. This is good, as it maintains biodiversity and as a biologist this is something that I think is important.

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Genetic recombination is achieved through reproduction. Sexual reproduction results in, arguable, the greatest genetic diversity as two distinct individuals copulate to produce genetically unique offspring. This just so happens to be the type humans are most familiar, mainly because we perform this kind of reproduction. With life being so very diverse on our planet, there has to be other forms of reproduction out there! And no, I don't mean sexual fetishes…

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I mean reproduction, or, the production of offspring. Some organisms reproduce asexually, meaning the genetic material inherited by the offspring is from a single parent. This type of reproduction is called parthenogenesis. This doesn’t necessarily mean that the offspring is a clone, although some organisms, mainly microbes, reproduce this way. In fact, some asexually reproducing species require copulation, or mating, to procreate. However, the paternal genetic material ultimately is ‘kicked out’ from the embryo. Talk about being used for sex.

 

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Parthenogenesis occurs when the progeny of an individual only has the maternal genetic material. A subset of parthenogenesis, gynogenesis ‘kicks out’ the paternal genetic material after mating, and therefore only the maternal genetic material contributes to the offspring’s genome. However, unlike parthenogenesis, species reproducing by gynogenesis must mate with a male (Schlupp et al., 1994). The schematic below sums up this nicely. M refers to maternal contributions, while P refers to paternal contributions (Schlupp et al., 1994).

Schlupp et al., 1994 Figure 1

Asexual reproduction implies that all the offspring will be genetically very similar to their parents. As the population is all female, the progeny will be as well (usually). But if it’s an all-female species, then how do they mate with males? It turns out theses females look to their close relatives to mate. The Amazon molly (Poecilia Formosa), a gynogen species, mates with either a male Atlantic molly (Pocecilia mexicana) or sailfin molly (Poecilia latipinna) in order to produce offspring (Marler and Ryan 1997).

http://www.txstate.edu/news/news_releases/news_archive/2013/August-2013/AmazonMolly082113.html 

Since, the male contributes no genetic material, I presumed there would be a very strong selection pressure against mating with a female who is literally using you for sex. Males mating with gynogens aren't increasing their fitness by having more offspring because the offspring produced aren’t genetically similar. So I would think that males would preferentially chose not to mate with Amazon mollies, or they would have to be coerced into mating with such an Amazon.

Male Atlantic and sailfin mollies preferentially chose to mate with their corresponding species, although sailfin mollies as less discriminating than Atlantic mollies (Ryan et al., 1996; Gabor and Ryan, 2001). Despite this preference, Amazon molly populations still persist. Therefore there must either be some sort of advantage male Atlantic or sailfin mollies obtain from mating with these females, or the males somehow mitigate the decrease in fitness caused by mating with a heterospecific, or a differing species.

In order to mitigate the cost of decreased fitness of mating with heterospecifics, male sailfin mollies employ two tactics. Firstly, as seen below, male sailfin mollies spent less time with Amazon mollies during the sailfin molly breeding season (Heubel and Schlupp, 2008). Correspondingly, there was a significantly lower proportion of Amazon molly juvenilles in the wild during the sailfin molly breeding season (Heubel and Schlupp, 2008). These figures show that when the availability of receptive sailfin molly females increased, male sailfin mollies ditched their second choice Amazon mollies and started spending time with females that would give them genetically similar progeny thereby increasing the male’s fitness.

Heubel and Schlupp, 2008 Figure 2

Heubel and Schlupp, 2008 Firgure 1

Not only do males’ preferences change by season, sailfin males further mitigate decreased fitness by sperm alterations. When males were exposed to Amazon mollies, they primed less sperm than males exposed to conspecifics, or females of their own species (Aspbury and Gabor, 2004). So sailfin males decreased their sperm viability in the presence of Amazon mollies in order to prevent unnecessary expenditure of energy. So not only do males ditch Amazon mollies during the sailfin breeding season, they also don’t spend as much energy on mating with Amazons as they do with sailfins… men right? Well really what can we expect when some females only use them for their sperm casing?

http://www.runningoffthereeses.com/2011/03/

Even though he’s not that into Amazonians, he, being sailfin mollies, still benefits from mating with them. Females witnessing a male mating become more ‘attracted’ to him, even if that male is mating with an individual of another species. So a female sailfin prefers a mating male sailfin. This preference persists even if that male is mating with an Amazon molly (Schlupp et al. 1994).  Mating, in general, will increase a male sailfin molly’s chance of perpetuating his genetic material because he will be more likely to mate with other females that have observed him mating. Perhaps this is why male mollies haven’t evolved to be completely discriminating in heterospecific mate choices. Even if he is mating with a heterospecific that will produce no genetically similar offspring, the chances of him mating with a conspecific will increase. A mating with a conspecific will increase his fitness so long as progeny is produced.

What could possibly further this behavior corresponds to other males witnessing a mating. Sailfin males copy other male’s mate choices. So if a male sailfin observed another male sailfin mating with an Amazon molly, he is more likely to mate with an Amazon molly was well (Schlupp and Ryan, 1997). It appears there is a positive feedback loop to mate with heterospecifics once an individual has mated with an individual of the opposite sex. This is at least partially the reason why this behavior hasn't been selected against.

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It appears the pros of mating with a heterospecific outweigh the cons. Which is important in maintaining the Amazon molly species. Ultimately, Amazon mollies rely on closely related mollies to ensure the species remains extant. If males weren’t as discriminating against Amazon mollies and in favor of their corresponding conspecifics, Amazon mollies would go extinct. If male sailfin mollies chose to mate with Amazon mollies and female sailfin mollies at the same proportions, Amazon mollies would become extinct (Heubel et al., 2009). Luckily for the Amazon mollies, males of the sailfin molly species aren’t so choosy. Otherwise that would mean Amazon mollies would go extinct by sex, or lack there of. Who would have thought death by sex is applicable in the natural world.

Click --> Death by Snu Snu

References

Aspbury, A.S. and C.R. Gabor. 2004. Discriminating males alter sperm production between species. PNAS 101(45):15970-15973.

Gabor, C.R. and M.J. Ryan. 2001. Geographical variation in reproductive character displacement in mate choice by male sailfin mollies. Proc. R. Soc. Lond. B 268:1063-1070.

Heubel, H.U., D.J. Rankin, and H. Kokko. 2009. How to go extinct by mating too much: population consequences of male mate choice and efficiency in a sexual-asexual species complex. Oikos 118:513:520.

Heubel, H.U., and I. Schlupp. 2008. Seasonal plasticity in male mating preferences in sailfin mollies. Behavioral Ecology 19:1080-1086.

Marler, C.A. and M.J. Ryan. 1997. Origin and maintenance of a female mating preference. Evolution 51(4):1244-1248.

Ryan, M.J., L.A. Dries, P. Batra, and D.M. Hillis. 1996. Male mate preferences in a gynogenetic species complex of Amazon mollies. Animal Behavior 52:1225-1236.

Schlupp, I., C. Marler, and M.J. Ryan. 1994. Benefit to male sailfin mollies of mating with heterospecific females. Science 263(5145):373.

Schlupp, I., and M.J. Ryan. 1997. Male sailfin mollies (Poecilia latipinna) copy the mate choice of other males. Behavioral Ecology 8(1

Neurosurgeon Creates Zombies

By: Brett Vassar

Meet the emerald jewel wasp, Ampulex compressa, a parasitoid wasp that hunts down cockroaches (Periplaneta americana) to provide a fresh meal for her offspring. This brightly colored wasp isn’t like the ol’ black and yellow wasps you may be thinking of that build nests for their houses. 

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The emerald jewel wasp is a natural born neurosurgeon who uses two extremely precise stings to inject venom into a cockroach’s nervous system, “zombifying” its prey. 

Fig. 1A (Libersat, 2003)

Fig. 2A (Libersat, 2003)

The first sting is directly into the thorax of the cockroach, causing a temporary paralysis of the front legs [Fig. 1A; right] (Libersat, 2003). Specifically, the first sting is targeted for the first thoracic ganglion of the cockroach's nervous system (Fouad et al., 1994). In cockroaches stung by C-14 radiolabeled wasps, radioactivity was significantly higher in the first thoracic (T1) ganglion as compared to T2, T3, and non-neuronal thoracic tissues [Fig. 2A; left] (Libersat, 2003). Fouad et al. (1996) conducted electromyograms (a technique for recording electrical activity of muscle cells) of the thoracic ganglion in the wind elicited escape response. This showed that in control cockroaches, in response to a wind stimulus, fast and slow motoneurons were stimulated in addition to rapid leg movements. Alternatively, in stung cockroaches, only a small burst in slow motoneurons are stimulated and no leg movements were observed [Fig. 5A; below]. This suggests that the stung cockroach wants to move, but they can't. 

Fig. 5A (Fouad et al., 1996)

Fig. 4A (Weisel-Eichler et al., 1999)

Fig. 1B (Libersat, 2003)

While immobile, the emerald jewel wasp makes its second surgical sting, this time, directly into the brain. The cockroach had only been transiently paralyzed from the first sting to the thorax. Sting two elicits an extreme behavioral manipulation where the cockroach goes into a phase of extensive grooming (cleaning of the outerbody surface, especially antennae) (Weisel-Eichler et al., 1999). Weisel-Eichler et al. (1999) showed this excessive grooming stage is caused by excessive stimulation of dopamine receptors in the central nervous system (CNS) of the cockroach [Fig. 4A; right]. Also, prior to a sting, Weisel-Eichler et al. (1999) showed if a cockroach given the dopamine antagonist Flupenthixol, grooming time is significantly reduced. Following an approximate 30 minute grooming period, the cockroach then enters a 2-5 week hypokinetic state (decreased bodily movement) characterized by long lasting lethargy [Fig. 5; right/below] (Libersat, 2003). The cockroach now cannot move, but simply stand frozen, alive. 

Fig. 5 (Weisel-Eichler et al., 1999)

Fig. 2 (Haspel and Libersat, 2003)

Fig. 1B (Haspel and Libersat, 2003)
br = brain, s = SEG

Now, how is it that the emerald jewel wasp is so precise in its second sting directly into the nervous system of the cockroach? Similar to identifying the thoracic ganglion as the target of the first sting, Haspel and Libersat (2003) had cockroaches stung by C-14 radiolabeled wasps and determined the site of the second sting as the subesophogeal ganglion (SEG) and the brain [Fig 1B, left; Fig 2, right]. It is believed that the venom contains components that directly affect neurons in the SEG and brain that control synapses in the thorax (Haspel and Libersat, 2003). Rosenberg et al. (2006) hypothesized that the venom injected into the brain affects monoaminergic neurons, specifically the neurotransmitter, octopamine. This is because octopaminergic (OA) neurons have previously been shown to play a critical role in the cockroaches escape behaviors (Libersat, 2003). In control, stung, and brainless cockroaches, the firing rate of (OA) neurons was significantly reduced in the stung cockroaches compared to the control, supporting the hypothesis of monoaminergic neurons and the hypokinetic state of the cockroach [Fig. 3; right/below] (Rosenberg et al., 2006). In a future study, Rosenberg et al. (2007) further confirmed their 2006 study by showing that stung cockroaches treated with an octopamine receptor agonist (CDM) had a significant increase in the time spent walking after being stung [Fig. 1; left].

Fig. 1 (Rosenberg et al., 2007)

Fig. 3 (Rosenberg et al., 2006)

So, what does the wasp do now that the cockroach stands motionless in place? First, she'll go seek out a burrow for the cockroach. What happens next is beyond awesome. It is important to note that although stung, the cockroach is not paralyzed, it's nervous system has been highjacked by the wasps venom. The wasp will grab one antenna and literally walk the cockroach to the burrow like a dog. If that ain't some zombie sh*t I don't know what is.  Take a look for yourself. 

Once in the burrow the female will lay a single egg on the underside of the cockroach, where the egg will hatch, and the larvae will feast off of the hemolymph (blood) of the cockroach, all while still ALIVE! The larvae will then enter into the cockroaches body and continue to feed of its insides until it fully develops into an adult male or female wasp. Once developed, the new offspring will emerge out of the finally dead cockroach exoskeleton. If the offspring is female, the process starts all over again. 

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Fig. 1E (Haspel et al., 2005)

Now that you know how this neurosurgeon injects its prey with venom, enjoy this video of the zombification process narrated by the one and only, Sir David Attenborough. 

http://biogeekery.files.wordpress.com/2013/04/ampulex-compressa.jpg

For more zombifying creatures, check out the fungus Ophiocordyceps unilateralis...

AND

the green-banded broodsac, Leucochloridium paradoxum...

Literature Cited:

Fouad, K., F. Libersat, W. Rathmayer. 1994. The venom of the cockroach-hunting wasp Ampulex

compressa changes motor thesholds: A novel tool for studying the neural control of arousal? Zoology 98:23-34.

Fouad, K., F. Libersat, and W. Rathmayer. 1996. Neuromodulation of the escape behavior of the cockroach Periplaneta americana by the venom of the parasitic wasp Ampulex compressa. Journal of Comparative Physiology A 178:91-100.

Haspel, G., and F. Libersat. 2003. Wasp venom blocks central cholinergic synapses to induce transient paralysis in cockroach prey. Journal of Neurobiology 54:628-37.

Haspel, G., E. Gefen, A. Ar, J.G. Glusman, and F. Libersat. 2005. Parasitoid wasp affects metabolism of cockroach host to favor food preservation for its offspring. Journal of Comparative Physiology A 191:529-34.

Libersat, F. 2003. Wasp uses venom cocktail to manipulate the behavior of its cockroach prey. Journal of Comparative Physiology A 189:497-508.

Rosenberg, L. A., H.J. Pflüger, G. Wegener, and F. Libersat. 2006. Wasp venom injected into the prey’s brain modulates thoracic identified monoaminergic neurons. Journal of Neurobiology. 66:155-68.

Rosenberg, L. A., J.G. Glusman, and F. Libersat. 2007. Octopamine partially restores walking in hypokinetic cockroaches stung by the parasitoid wasp Ampulex compressa. Journal of Experimental Biology 210:4411-4417.

Weisel-Eichler, A., G. Haspel, and F. Libersat. 1999. Venom of a parasitoid wasp induces prolonged grooming in the cockroach. Journal of Experimental Biology 202:957-964.

Videos/Images:
https://www.youtube.com/watch?v=piht4yT57MY
https://www.youtube.com/watch?v=UWAV1zj5TXQ
https://www.youtube.com/watch?v=vl_9kghmChw
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