[Odonata-l] Why report hindwing length and not forewing length also?

[Ola Fincke]

All my measurements are on live insects, so I just measure from the  
tip to the base of the wing (i.e. end of the wing itself, not the  
structure into which it inserts).
To do the abdomen, I just tap it straight and measure. Obviously  
there's more error measurement associated with that measure, than the  
wings.
I have also done wet weights, to get correlations among wing, abdomen  
and wet weight (all are highly correlated).  Brad Anholt has done a  
lot of the latter.

Ola

Ola Fincke
Dept. of Zoology
University of Oklahoma
Norman, OK 73019
Tel: 405-325-5514
Fax: 405-325-6202




On Mar 17, 2007, at 1:48 PM, Nick and Ailsa Donnelly wrote:

> This interests me a lot, because I have been measuring Odonata for  
> many years.
>
> One problem with wing measurement is that it is not certain where  
> the base of the wing is located.  In my recent Orthemis study I  
> have been taking the notch at the base of the costa that seems to  
> correspond to the major point of flexure of the wing.  This is  
> pretty difficult to observe if one is using a millimeter scale on a  
> specimen held beneath the microscope, but it can be done.  Tillyard  
> more or less shows where it is, but he does not figure it worth a  
> damn.  My technique is to scan the wing and scale together, and  
> then to transpose the scale image on to the wing in Photoshop,  
> rotating and translating the scale to make the measurement.  In  
> this way I can get about 0.1 mm repeatability.  This is great for  
> my own exercises, in which I wish to show comparisons with other  
> specimens measured also by me.  But how do I compare my results  
> with those of others?  The simple answer is that I cannot do this,  
> because I have no idea how others measure wings.  So, how do you do  
> it, and from where?
>
> And abdominal measurment - don't even talk about that.  Even when  
> the abdomen is still in one piece, and it is straight, not curved,  
> there is the problem of shrinkage during preservation.  This  
> measurement is vastly less certain than wing measurement, and I use  
> the hind wing as the only more or less reliable surrogate for  
> size.  I still am not quite certain what all this is  
> accomplishing.  I found in the Orthemis study one specimen for  
> which I thought I had made a serious mistake - it couldn't really  
> be shaped like that, with such short wings and a long abdomen.  I  
> pulled the specimen out and looked  at it again- It really was  
> shaped like that - long abdomen and short wings.  No mistake at  
> all.  But what was the meaning of its reported size?
>
> What I would like to see done is weight measurements.  I once found  
> a species of Nesobasis (damselfly) for which the males tended to be  
> much larger than the females.  I estimated from dimensions alone  
> that the males must weight at least twice what the females weighed,  
> which I think is remarkable.  But a protocol for weight measurement  
> would be very difficult and would have to involve taking a very  
> portable and accurate scale into the field.
>
> A digression.  Years ago I was in my office when the friendly  
> Fishers sales rep wandered in.  "What do you have that is new and  
> interesting?". I asked.  "Why we have just introduced portable,  
> digital, battery powered scales", he said with considerable pride.   
> "I'll bet the drug dealers are scarfing them up", I replied.  He  
> promptly turned an interesting shade of gray, never having  
> considered this marketing possibility.
>
> From: odonata-l-bounces at listhost.ups.edu [mailto:odonata-l- 
> bounces at listhost.ups.edu] On Behalf Of Ola Fincke
> Sent: Thursday, March 15, 2007 4:16 PM
> To: Mike May
> Cc: Odonata-l
> Subject: Re: [Odonata-l] Why report hindwing length and not  
> forewing length also?
>
> In many species, it's well-known that size declines over the  
> season, which is one reason that those of us interested in the  
> effects of size on reproductive success take that into account  
> (e.g. Fincke & Hadrys 2001; see also work by Dave Thompson and  
> others, cited in the former).
>
> There must be a LOT of geographic variation in size; certainly  
> Ischnura verticalis in MI is much larger than it is in OK. Even  
> within species in similar areas, size can vary quite a across  
> populations. I am collecting data on this within Enallagma.
>
> Ola Fincke
> Dept. of Zoology
> University of Oklahoma
> Norman, OK 73019
> Tel: 405-325-5514
> Fax: 405-325-6202
>
>
>
>
> On Mar 15, 2007, at 1:52 PM, Mike May wrote:
>
>> Dennis, et al.,
>> I have to agree that a much more useful set of measurements,  
>> regardless of which body parts are selected, would be mean +/-  
>> standard deviation (range). Likewise it would be great to include  
>> much more precise distribution data (e.g., county rather than  
>> state level - hooray again for Nick Donnelly's dot maps) and  
>> seasonal data (e.g., flight season at several different latitudes  
>> or within regions of similar climate). The reason for not doing so  
>> in NWM and W&M is simple, and the same in all these cases - time  
>> and effort. To a fairly accurate approximation, one can (read,  
>> "Mike can") riffle through the hundreds of specimens of Enallagma  
>> civile at FSCA, pick out several of the largest and smallest from  
>> different regions, spread them out and compare by eye, select and  
>> measure 3-4 at each end of the size range, and write down the  
>> maximum and minimum results. That's exactly what I did, and,  
>> although tedious enough, it's a lot quicker than selecting a  
>> random sample large enough to be statistically relevant (~30),  
>> measuring (with a mm ruler, sometimes viewed through a scope) and  
>> recording all of them, and calculating the appropriate statistics.  
>> That doesn't make the former technique great, especially if one or  
>> two atypically large or small individuals are incuded, it's just  
>> easier. There's also no doubt that that human error plays a role  
>> and is likely to lead to a more misleading outcome in assessing  
>> range than aggregated statistics. As an aside, total length and  
>> abdominal length are probably much more subject to error than is  
>> wing length because of the tendency of heads to fall off, abdomens  
>> to curl, etc.
>> Anyway, I think a genuinely worthwhile project would be to  
>> accumulate and publish careful size measurements of as many  
>> odonate species as possible, based on statistically meaningful and  
>> geographically diverse samples. This just wasn't feasible in doing  
>> the manuals, but it would be very useful in itself and could lead  
>> to some interesting questions. E.g., does size vary geographically  
>> or seasonally, and is the variation consistent across species?  
>> This has been shown to be true for several species, as Dennis  
>> notes, but the answer isn't known for most. If such patterns do  
>> exist, then you can ask why. If anyone is interested in  
>> undertaking such a project, I'd be glad to give them the benefit  
>> of my experience, for what it's worth.
>> Mike May
>> ----- Original Message -----
>> From: Dennis Paulson
>> To: Odonata-l
>> Sent: Wednesday, March 14, 2007 12:17 PM
>> Subject: Re: [Odonata-l] Why report hindwing length and not  
>> forewing length also?
>>
>> What is sometimes frustrating is that guidebooks such as these  
>> list measurement extremes without giving any idea of means or  
>> explaining the significance of the extremes, and the handbooks  
>> Alex mentioned are among the best examples of this.
>>
>> For example, I opened Needham, Westfall & May to a page at random  
>> and found Erpetogomphus bothrops. Length 38-51 mm, abdomen 26-39,  
>> hindwing 21-31. This is a common species in Sonora, which I've  
>> visited several times in recent years, and I always thought the  
>> individuals I saw and collected didn't vary anything like that. So  
>> I just measured the hind wings of all my specimens (from  
>> throughout the range of the species) and found this:
>>
>> males - range 23-26.5 mm, mean 24.9 (n=15)
>>
>> Eleven were with n 1 mm of the mean, in the range 24-26 mm.
>>
>> females - range 26.5-29 mm, mean 27.5 (n=6)
>>
>> Five were within 1 mm of the mean, in the range 26.5-28.5 mm.
>>
>> Thus in both sexes, the great majority of individuals measured  
>> within a 2-mm range, and that range defines the size of each sex  
>> quite well. Combining the sexes would justify listing the range in  
>> "usual" hindwing length of 24-28.5 mm. Total length and abdomen  
>> length don't seem to vary any more than hindwing length.
>>
>> The entire series of 21 individuals ranged from 23-29 mm. Rosser  
>> Garrison, in his 1994 revision of the genus, examined 91  
>> specimens. He listed the variation in hindwing length as 27-31 mm,  
>> which makes me wonder if we measure wings differently. In fact we  
>> must, because some of my specimens were among those he measured.  
>> Both of u show a considerably smaller range than that listed in  
>> NWM, but between my measurements and Garrison's measurements,  
>> we're approaching the range in NWM, so part of the great variation  
>> listed in that book could be explained by different      
>> measurement techniques and/or acquiring the measurements from all  
>> published data. Unfortunately, ranges like that don't give one a  
>> very good idea of how big the dragonfly is. Perhaps Mike May can  
>> tell us how those figures were obtained. I emphasize that I'm not  
>> criticizing NWM, as I'm sure the authors of that book did the best  
>> they could in acquiring these figures.
>>
>> I do know, from much research on bird size, that guide book  
>> writers sometimes get it wrong, and the incorrect figures have a  
>> life of their own, copied from book to book. I found total length  
>> measurements off by as much as 15% when analyzing measurements in  
>> several bird guides, at times a larger species listed as smaller  
>> than a smaller species. How many bird-b ok writers nowadays  
>> measure birds, live or dead?
>>
>> In many taxonomic papers, the author measures a series of  
>> specimens and gives ranges and means, but for many species there  
>> are no such papers, so writers of guide books have a difficult  
>> time getting measurements, with two options. Either they have  
>> access to a collection and spend long hours measuring specimens,  
>> or they take the figures from other publications, the research  
>> literature and/or other guide books. One of my colleagues recently  
>> confessed to me that when he listed measurements for a book on  
>> dragonflies, he just used the midpoint of the measurements in NWM  
>> and Westfall & May, which seems as good a way of doing it as any.  
>> I think having a single measurement in a guide book makes it  
>> easier to picture the size of the animal than when there is a  
>> rather substantial range.
>>
>> Some species vary in size over the season. Pachydiplax longipennis  
>> t at emerge in summer in southern Florida have hind wings about 3  
>> mm shorter than those that emerge in the winter, and the size  
>> varies seasonally at least as far north as the US Gulf states. I  
>> am not aware if seasonal variation has been established for other  
>> species. Just from eyeballing it, it seems to me that some species  
>> vary more in size than others, but perhaps that just depends on  
>> how many of them you see. I was just examining two Sympetrum  
>> costiferum, one of which seemed no more than 2/3 the bulk of the  
>> other, and two Enallagma carunculatum, one of which was surely  
>> only half the bulk of the other and about 2/3 its length. These  
>> are unusual extremes, of course. When I look at my collection or  
>> at odonates in the field, individuals of a species mostly look  
>> around the same size.
>>
>> Another source of variation in odonates is temperature.  
>> Damselflies in Mexico and Central America tend to be larger at  
>> higher elevations, presumably something about temperatu e vis-a- 
>> vis development time of the larvae. I don't know if there is  
>> latitudinal variation as well, but there should be. Nick Donnelly  
>> called attention to the very small size of some damselflies in  
>> eastern Texas, and I have seen these same populations of  
>> impressively tiny creatures. I don't know whether these  
>> populations are genetically distinct, or does some environmental  
>> factor of the area have them emerging at a smaller size? I  
>> collected tiny Perithemis mooma in Yucatan, as small as or smaller  
>> than Nannothemis bella.
>>
>> There are probably many more examples of interesting size  
>> variation in odonates, and it would be good to know more about this.
>>
>> Dennis Paulson
>>
>> On Mar 14, 2007, at 6:58 AM, Mike May wrote:
>>
>>> Certainly part of the reason is tradition. Once a large body of  
>>> data is
>>> available for a particular measurement, the value of that  
>>> measurement for
>>> comparative study is enhanced. I suspect, also, that the hindwing  
>>> may have
>>> been selected originally because, when a dragonfly is held in the  
>>> hand with
>>> the wings pressed together above the back, the hindwing is  
>>> positioned
>>> outside the forewing. Although the forces produced by fore- and  
>>> hindwings in
>>> flight are certainly somewhat different, I feel pretty confident  
>>> that had
>>> nothing to do with the decision.
>>>
>>> The forewings are nearly always slightly longer than the  
>>> hindwings. My
>>> impression is that the proportionate difference does not vary  
>>> greatly with
>>> size, taxon or sex, but I don't know whether this has been  
>>> investigated
>>> rigorously. Females do typically have longer wings than males in  
>>> comparison
>>> to other measures of body size such as total length or thoracic mass
>>> (probably because abdominal mass becomes greater in mature  
>>> females because
>>> of the mass of eggs), but I don't know that the differences  
>>> between fore- < SPAN>
>>> and hindwings is affected by sex. Maybe Roy Beckemeyer can  
>>> illuminate that
>>> question a bit more.
>>>
>>> Mike May
>>>
>>> ----- Original Message -----
>>> From: <aardila at uoguelph.ca>
>>> To: "Odonata-l" <odonata-l at listhost.ups.edu>
>>> Sent: Wednesday, March 14, 2007 4:28 AM
>>> Subject: [Odonata-l] Why report hindwing length and not forewing  
>>> length
>>> also?
>>>
>>>
>>>> Hello everyone,
>>>>
>>>> I have the books "Dragonflies of North America"(Needham,  
>>>> Westfall ,and
>>>> May, 2000) and "Damselflies of North America" (Westfall and May,
>>>> 1996). These books are excellent. They report the body size lenght,
>>>> abdomen lenght, and hindwing length for every Odonata species in  
>>>> North
>>>> America.
>>>>
>>>> However, I don't understand why the size of the forewings is not
>>>> reported. Is this by convention? What is the history behind  
>>>> this? Why
>>>> were the hindwings and not the forewings chosen? Is there a
>>>> statistically and biologically insignificant difference between the
>>>> forewings and the hindwings within species (and sex) in  
>>>> Odonates? Is
>>>> this selection based on the role of the hindwings in flight? I  
>>>> would
>>>> appreciate any guidance that could help me find an answer to these
>>>> questions. Thank you.
>>>>
>>>> Alex
>>>>
>>>> --
>>>> Alex Ardila-Garcia
>>
>> -----
>> Dennis Paulson
>> 1724 NE 98 St.
>> Seattle, WA 98115
>> 206-528-1382
>> dennispaulson at comcast.net
>>
>>
>>
>>
>>
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