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Maydianne Andrade: Expert Q&A

On July 13, 2009, biologist Maydianne Andrade answered questions about poisonous spiders and praying mantises, cannibalism and adaptive suicide, teaching evolutionary biology, and more.


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Q: Hi Maydianne,
I loved the show. Here's my question: Is it possible to tell if a spider is poisonous just by looking at it? Would I be able to tell the safe ones from the dangerous ones? Sophie L. (age 10), Winchester, Massachusetts

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Maydianne Andrade: Hi Sophie,
I am glad you enjoyed the show!

All spiders have venom, but only a few have venom that can hurt humans. I am afraid there is no easy way to tell if a spider is dangerous for humans just by looking at it. Although many poisonous creatures show 'warning colouration' like the black widow (black and red), some are just plain old brown or grey! I see you are writing from Massachusetts—as far as I know, there are only two poisonous spiders there: (1) the black widow, which is black and (like all black widows) has a red 'hour glass' mark on the underside of its body, and (2) the Brown Recluse, which unfortunately is just brown and resembles a lot of other spiders. Luckily, both of these are fairly rare in your area.

Q: Hi,

We were so thrilled to see you on TV. We are interested in the procedure used to measure the amount of semen the male spiders are able to inject. Scott Hoyland, Victoria, British Columbia, Canada

Andrade: Hi Scott,
Great to hear from you!

Female spiders store sperm in special organs. They retain the sperm throughout their lives. We measured sperm transfer by removing storage organs from females and counting the number of sperm in them (using a microscope and special slides usually used for counting blood cells). We manipulated the duration of mating (by interrupting the male and female at various times) and then compared the number of sperm transferred to see whether it was related to the time the male spent mating. We also counted stored sperm after natural matings.

Q: Maydianne:

I am a firm believer in evolution but confess I don't understand how a specific behaviour like the male spider's sacrifice during sex can be passed on to his offspring. How can a behaviour as specific as this be inherited? Thanks! Mike Patenaude, Winnipeg, Manitoba, Canada

Andrade: Hi Mike,
Behaviours, like other traits, develop as a result of the interaction of genes and the environment. For example, your genes may have included a 'recipe' that allowed the possibility that you would be 6'5'' tall, but you would only attain this height if your diet as a child was sufficiently nutritious. At the same time, someone with a genetic recipe for an adult size of 5' will not be 6'5'' no matter what his childhood diet. Behaviours are similar in that an individual's genetic make-up can define the range of behaviours that are possible for that individual. This is true even though behaviours are generally flexible, by which I mean behavioural decisions are often adjusted as a function of minute-to-minute assessment of relevant aspects of the environment—an individual's genetic 'recipe' can still affect the range of possible responses they will have to a particular set of conditions (e.g, a pit bull and a golden retriever can be raised under virtually identical conditions, but they are unlikely to have the same temperament). This has been confirmed for a range of different types of behaviours in different animals, and there is particularly nice work in mice and fruit flies. For example, a genetic basis has been demonstrated for variable, complex behaviours such as the amount and type of care offered to offspring, and nest-building behavior in mice. Behaviour genetics is a fascinating and rapidly expanding field.

In the case of Australian redback spiders, the self-sacrificial somersault during normal matings appears to have a genetic basis. For example, male redbacks 'somersault' even when paired with females of their closest relatives, the New Zealand katipo spider (a species in which males never somersault).

Q: Spiders freak me out! My question: What in the world drew you to working in this field? Also, have you ever accidentally been bit by a black widow? Matthew, Chicago, Illinois

Andrade: Hi Matthew,
Spiders used to freak me out too! In the end, I started working on them because they were just the best research subjects for the questions I wanted to answer. I just toughed it out in the lab until I got over my fear of them!

I have never been bitten by a black widow. We have a lot of safety protocols in the lab and field to try to avoid this. I have met several Australians who have been bitten, though, and it sounds like it can be very painful.

Q: Hi Maydianne,
I am also a fan of spiders. I have a few questions: Do you think that arachnophobia is learned or innate? After working with spiders, would you consider working with another animal? Besides spiders, what is another arthropod that you like? Thanks. Melissa , Cleveland, Ohio

Andrade: Hi Melissa,
I think arachnophobia is learned, but I have no real scientific basis for this conclusion! Certainly, when I visit school groups of various ages, I see much less fear of arachnids in preschoolers to grade 3 kids than I see in older children. I suspect it would take only a few strong negative responses from a parent to condition their child to fear spiders.

I have also worked on crickets and fish, and I would consider working with any animal that would allow a focus on questions in which I am interested (although insects and spiders are nearest to my heart). I have always thought it would be fascinating to work on fireflies. I have a friend who worked on them for years and now can mimic firefly courtship calls using a flashlight. So he can go out in the field and 'talk' to them! Amazing.

Q: Are there cases in nature in which males eat females during or after mating rather than the other way around as in redbacks? An anonymous male

Andrade: Dear anonymous male,
Although I have seen the odd report of males eating females after mating, it seems to be very rare. This type of behaviour would be very (evolutionarily) costly for males since the female would be unable to produce offspring after the male invested energy and time in courting and mating with her.

More common are reports of males eating females during courtship, or after a failed courtship. For example, in some experiments we are doing now with a local jumping spider, if a female rebuffs a male's attempts at mating, he may then kill and eat her.

Q: Do male redback spiders mate but avoid getting eaten? I assume this means fewer sperm are transmitted, but he survives to mate again. Vince Simeon, Richmond, California

Andrade: Hi Vince,
There is such a high likelihood of dying during the search for females that even surviving males would not likely have the chance to mate again. What we see in nature is consistent with this. Although redback males do sometimes survive mating, they rarely leave the female's web and will often die there.

Q: Is the behavior you see in your spiders the same as the behavior of praying mantises? Thanks! Eliza Lehner, Milton, Massachusetts

Andrade: Hi Eliza,
No, this is a very different behaviour. Male mantids mount the female in a way that leaves them relatively far away from her mouthparts, and they typically attempt to leap away from the female after mating. So this behaviour is not interpreted as male 'self sacrifice.' There was an interesting article in The New York Times a few years ago on research in this area, see:

Q: I know that the praying mantis is famous for eating its mate, but are there other species of insects (or animals) that use sexual cannibalism as a reproductive strategy? Are there any other examples of adaptive suicide? Anonymous

Andrade: Hello,
Sexual cannibalism is seen in a number of spiders and in the praying mantis, but otherwise it is relatively uncommon in nature (although I have seen a couple of reports of sexual cannibalism in snakes).

Adaptive suicide is seen in social insects on a large scale. For example, a bee will give up her life by stinging you in defense of her colony.

Q: What is the most difficult or challenging aspect of your work as an evolutionary biologist? Rebecca Safford, Lynnwood (near Seattle), Washington

Andrade: Dear Rebecca,
In terms of research, it is balancing the competing demands (intellectual, practical, financial) of multiple research projects and graduate students, each of which I find fascinating. In terms of teaching, it is overcoming the (often erroneous) preconceptions and prejudices of students about evolutionary biology.

Q: If the male redback survives the first bite from a female, why would he go back a second time? Wouldn't he have a better chance of having more offspring if he mated with a second, different female (even if that one ultimately did him in)? Dan, St. Louis, Missouri

Andrade: Dear Dan,
The male could perhaps do better if he could mate with two different females, but that is not an option that is available to most males. The probability of surviving the trip to a female is pretty small (less than 20 percent of males make it at all). Once the male gets there, he has to convince the female to mate with him (not his competitors), and hope that she has not already mated. This is particularly important because male redbacks leave plugs inside the female after mating. The plugs do not prevent the female from laying and fertilizing eggs with his sperm, but they prevent other males from fertilizing those eggs. Now, one other strange detail about these spiders is important here: the female stores sperm in two separate storage organs and can fertilize eggs using stored sperm from one mating for her entire adult life. If the male mates twice with a female, he plugs both of these organs and will fertilize almost all of the female's eggs even if she later mates with another male. So all in all, mating twice and being killed may ensure the male has more offspring overall.

Q: I'm just happy to see a young, smart, attractive African-American woman who's taken an interest in something as interesting as spider biology and has stuck with it. I'm currently in a masters program in health management at Johns Hopkins, and I remember my professional "evolution," as it were, started from my love of animals and how I used to study their behavioral characteristics in middle/high school. Then came college, and I wanted to be a doctor, so I took biology (which was great). Between then, bills, and other influences (including my own goals of being a surgeon) I find myself working on the business side of medicine. I love it, but I always wonder what it would've been like to pursue the "first" dream of studying animals. Best of luck to you, and I hope you accomplish your goals. C. Talley, Baltimore Maryland

Andrade: Hello,
Thank you! I am certainly glad I took this path instead of others, but sometime wonder what would have happened if I had become a pediatrician (my own 'first' dream).

I am often asked to address young people (and sometimes their parents) about being a woman and/or visible minority in science. One of the main messages I try to get across is the importance of pursuing your interests if you can, even if they take you down the 'path less traveled,' and even if you have never seen someone like you in a similar role. Support of family and friends is also critical in this. I have been incredibly lucky that my family and friends have always supported my efforts, even if my goals seemed bit bizarre to them!