Dear Vivek,

innate oviposition preferences are not uncommon in insects. There are some well documented examples of specialized Drosophila species that illustrate, how innate preferences may have evolved and how the external and internal olfactory organs are affected by spezialization or host shifts.

To gain a better insight in this topic, I recomment the following papers:

Linz et al (2013) Host plant-driven sensory spezialization in Drosophila erecta. Proc R Soc B 280

Ibba et al (2010) Macroglomeruli for fruit odors change blend preference in Drosophila. Naturwissenschaften 97

Dear Svea, thank you, but It's still not clear !!

Oviposition preference is the interplay of both gustatory and olfactory modalities, whereas in our study we found a olfactory led oviposition stimulation. Meaning the stimulant alone was enough to instigate flies to lay eggs. I have read the articles you have suggested , but, could not find my answer.

The following paper may help to shed some light :

Facknath, S. and Wright, D. 2007. Is host selection in leafminer adults influenced by pre-imaginal or early adult experience?. J. Appl. Entomol. 131(8), 505–512.

Hi Vivek,

odor cues related to food, oviposition sites, etc, can trigger behavioral responses in insects in two ways: a) innately, through physiological processes that grant detection, information processing and output triggering without the need of previous experience and, b) only through experiencing a set of previous events that allow the organism to establish an association between the presence of an odor and a reward (success in any terms, like nutrient gain, for example).

As Sven said, innate oviposition preferences seem to be quite common. In your case, it is not clear to me why you consider these observations a case of learning by the flies. The fact that flies not exposed previously also oviposit in a similar way indicates that it might be a case of an innately driven behavior. One would guess thay If you are a fruit fly, you need to be very efficient in recognising such a relevant resource without need of learning, I guess. Of course learning may improve oviposition performance! But that is a different issue.

To my knowledge, neurophysiological experiences have never been demonstrated to affect genes in any way as to be inheritable. So I would exclude such a hypothesis on the basis of current scientific theories and evidences. It would require complex mechanisms altering gene sequences in particular ways that would promote specific behaviors. This is not supported by any evidences in any fields of neurobiology, as far as I know. So, it seems this cannot be a template aquired after maternal experience.

I hope these observations clarify some of your doubts.

Thank you all for enlightening me on the topic. However, my doubt on the word "Innate" is not clear. Innate means congenital or inborn. How can we deny that innate behaviours are not on the basis of genetics. How will a organism know to do certain things without learning or previous exposure? Won't the traits of such behaviour be passed on from the parents?

Vivek,

your question on " How will a organism know to do certain things without learning" is on the very basis of ethology. This is one of the aspects of the foundational work done by Konrad Lorenz and Niko Tinbergen (their work made them Nobel prize winners together with Karl von Frisch in 1973).

In fact we assume that behaviors called innate are based on genetically tranferred information contained in a species genome (which can, of course, have variability in certain genes/behaviors).

How this sets of genes determine behavior is currently a very "hot spot" in neuroscience. This means that we still mostly base our opinions on single gene models. For a real picture to be good enough we still need to work on gene networks, which might be a better basis to understand complex outputs such as behavioral or physiological traits. Unfortunately, the whole mechanistic view is not available to answer your question properly, but this does not disqualify the opinion that an innate behavior is a genetically based set of neuronal and motor responses triggered by key stimuli recognized by specific sensory receptors which are there probably due to selection pressures favoring their role.

All the best,

You can look up the Baldwin effect and also epigenetics. It is known for example that in humans the surplus or absence of food your grandmother experienced determine your metabolism - i.e. when your mother is born her egg cells have the epigentic information from her mother (aka your grandmother). By methylation certain genes will be more active than others and hence influence in this case metabolic rate. If this stays on, the epigentic changes can become permanent or the default, that is a brief and incomplete description of the Baldwin effect. Importantly it also applies to learning. Whatever is constant in the environment can be laid down, i.e. how insects respond to rain (not a good idea to fly in rain). Whatever is random and unpredictable is not worth to learn. Everything inbetween especially constants within the lifetime of an insect but not necessarily constant for the next generation is accomplished through associative learning (if the cue is important enough, flies do not learn car smells).

Thanks Gerit for your input on the subject. In fact I think we have a long way to go on these grounds! A link between epigenetics and insect behavior would be really interesting in order to shed some light on whether experiences suffered by one generation can somehow modulate the behavior of the following generations. You are right, as a link has been established between metabolic diseases and epigenetics. Nevertheless, I am not informed on whether a similar case has been established for behavioral traits (specially in insects). Do you know of any such links?

Sure there is, shown first in rats. Stress response of pups later in life depends on mothering - epigenetically "priming" (see review by Miller, Science 2010). And I would not be surprised if some insects show different behaviour as adults given stress during larvae or pupae stage. Experience of high predation pressure indirectly (like bat calls in moth) may prone them to early risky mating rather than more selective mating - though that is speculation and our lab lacks the genetic tools but behaviourally we plan to look at that.

Thanks for your answer! Fine, this is in fact very relevant and a completely new perspective for many behavioral biologists! I really look forward to see new links between behavior and epigenetics.

Still, regarding Vivek's question. I guess epigenetics are difficult to connect with classical learning, don't you think? I would still say that odor recognition is expected in many organisms when talking about food items or other relevant resources.

Thank you all for the wonderful discussion. The answers are very much convincing and has increased my knowledge about this aspect. A special thanks to Marcelo. I have one more doubt in mind. Our test insect Bactrocera dorsalis is polyphagous. We have isolated 4 oviposition stimulants from 4 different plants. This insect has more than 300 hosts. The 4 cues we isolated are triggering innate oviposition behavior. So is it possible that all 300 hosts of this insect to have oviposition stimulants? How can a insect co-evolve with such large number of plants ?

Vivek, how about common odorants (and tastants) or very similar ones present on host plants and detected by the same set of receptor neurons, maybe? The question then would be, is Batrocera able to tell them apart? Or do they basically mean a broadly identical sensory object? I think your last question seems testable. Did you look for these 4 cues in different known host plants? I would choose several (4 or 5?) host plants and search for these or any other common odorants... those may include the key compounds.

Ok Marcelo let me tell you how the experiments were carried out. We selected 50 host plants (but have only finish working on 4). We did a head space collection of the fruit volatiles and did a GC/MS/MS of the same. We then tested each cue for its oviposition stimulantion activity. We rounded of 4 cues that were triggering innate oviposition responce. We found that the 4 cues were specific to the plants from which they were extracted. Although, our results are priliminary, we think either a set of receptors must detect many odorants or there are specific circute for each cue. B. dorsalis genome is not sequenced and its a disadvantage for us to go indepth about the receptor neurons.

Another theory for all to consider is the Hopkin's Host Selection Principle, which was at one point in time hotly contested, but is now making a comeback following recent developments in technology and availability of highly sensitive instruments for measuring minutes amounts of plant volatiles and insect response to these through the use of electroantennograms.