Marisano James

Brief Bio

Figure 0: Photo of me taken at a beach cleaning event.

I’m a Ph.D. candidate in the Population Biology Grad­u­ate Group at the Un­i­ver­si­ty of California, Davis. Be­fore joining the Eisen Lab, I attended under­grad at Frank­lin and Mar­­shall College, then worked as a soft­ware de­vel­op­er in the computer industry, before re­turning to university and graduating from In­ter­na­tion­al Un­i­ver­si­ty Bremen, in Bremen, Germany (now Constructor Un­i­ver­si­ty), where I majored in Com­pu­ta­tion­al Bi­ol­o­gy and Bioinformatics. I originally expected to study virus evolution or the ear­ly evo­lu­tion of eu­kar­y­otes in graduate school, but was lured away to the macro side by a class on the evolution of senses. [So, I’d say the Eisen Lab moniker should be some­thing more like, “Mainly microbes, all the time.”] I mostly work on in­sect vision—particularly that of adult male Strep­sip­tera—but have also branched out into flight kin­e­ma­tics to better understand strepsipteran visual requirements.

Research

Figure 1: Comparison of the morphologically typical compound eye of a Drosophila (a true fly) with that of a Halic­to­pha­gus Strep­sip­tera. A) Small abutting facets constitute the compound eyes of this drosopholid, each resolving a single pixel. (However, note that nearly all true flies employ “neural superposition,” in which off-axis light that would have been blocked by the recipient facet is redirected neurally (not optically) to a neighboring facet for which it is on-axis. This improves light sensitivity by about 6×, without degrading acuity at all. Because of this enhancement, flies are not an ideal reference point. However, Drosophila are extremely well-studied, and for this external assessment the comparison is sound.) B) The ‘facets’ of this Strepsiptera are clearly separated, and also much larger, because each ommatidium contains an extended retina, onto which a multi-pixel image may be projected. Because of such differences, the facets of an adult male strepsip­te­ran’s eyes are sometimes referred to as eyelets. Notice that the ventral eyelets are much larger than the dorsal ones. This may represent a so-called acute zone of superior visual resolution; however, it may also normally scan an area from which less light is incident, so that a larger eyelet surface area is required to collect enough light in the same amount of time. (A) was taken from [2]. (B) from [3].

All this peculiarity and potential ‘extra’ visual effort invites one to ask why it occurs at all. What does an adult male Strepsiptera obtain from having such eyes? (BTW—adult females are blind, wingless, legless, and lack antennae¹; but then, emerged adult males starve to death in a few hours…) How well can they see? How did their eyes evolve and why has this eye morphology been retained in Strepsiptera, while its expected enhanced acuity has not been reproduced in other insects? To address these questions I’ve been investigating Xenos peckii, a diurnal species, and Elenchus koebelei, a crepuscular species. Among many fascinating attributes, Strepsiptera are one of the few insect orders in which the same eye design is used exclusively in all three major light regimes: photopic (broad daylight), mesopic (dawn or dusk, i.e., crepuscular), and scotopic (late night). Thus, I have designs to work with a nocturnal species too. Stay tuned!

¹ ^This is true of all but the most basal extant lineage in which strepsipteran females retain eyes and legs. In that single clade, adult females leave the body of their host; however, they are still severely lacking in mobility and do not oviposit. This general inability to oviposit freely has led to all strepsipteran females giving birth to live young that seek out their own hosts.

Adult male strepsipteran morphology

Surprisingly, the wings were not the source of the name of the order, or its common English name, “twisted-wing parasites”; the warped condition of the halteres was, which were then thought to be elytra, and were known to be sensors: “Strepsiptera is the term I propose by which to designate the order, which name I have given it on account of its distorted elytra” [4]. Somewhat subsequently, the halteres were thought to be twisted forewings (e.g., forewings that fail to unfold) that no longer provide meaningful lift or any sensory input, but were still considered useful for enhancing the excitatory state of the insect. Later, after dipteran halteres were better understood, strepsipteran ‘forewings’ were revisited and found to act in a similar manner. Hover over the buttons or the body parts depicted in Figure 2 below for more intriguing facts about strepsipteran mor­phol­o­gy.

Nocturnal Strepsiptera

² ^Some folks might want to call this (sub?)species T. mexicana; I, however, side with Dr. Cook [6], who is a taxonomist and seems to have seen enough of both to make consistent distinctions.
³ ^The family Myrmecolacidae is incredibly interesting because it consists entirely of split host infectors: male Myrmecolacidae infect ants (thus, the name of the family—most often fire ants) and females of the same species infect Orthopteroidea (most often crickets—but also mantises(!), etc.) [7,8].

Triozocera texana in flight

By carefully observing an insect fly, you can get a sense of what it can see and by extension, what it needs to be able to see. You can also obtain an indication of how fast it flies—although that can depend on what task is being attended to—which is also an important visual parameter. In general, bearers of simple eyes are either masters of vision in low-light (think spiders, most centipedes, etc.), or they have relatively slow eyes with high acuity in a limited field of view. Those with compound eyes have comparatively awful acuity, but are capable of seeing very quickly in all directions at once. However, in many ways my having photographed flying Triozocera texana is a prelude to photographing even tinier Strepsiptera, en route to strepsipteran videography, which should much more completely address strepsipteran flight capacity and its supporting optical system. (Dare I say, “Stay tuned”?) Following are some photos of T. texana freely flying in the field that I captured using a highly modified commercial insect rig. To my knowledge, these are the first still images of Strepsiptera in flight.