Flight Capacity and Response to Habitat Drying of Endemic Diving Beetles (Coleoptera: Dytiscidae) in Arkansas (USA)

Round 1

Reviewer 1 Report

The study described in the manuscript aims to assess the flight capacity and the response to drying of two species of Dytiscidae in an experimental set-up. The study is straightforward and well written. Due to the limited distributions of the species, the study could have important implications regarding the conservation of the beetles and their habitats.

I have just very few minor comments:

l. 31: Please add the year of publication behind the authority at first mentioning of the species: Heterosternuta sulphuria Matta and Wolfe, 1979; Heterosternuta phoebeae Wolfe and Harp, 2003

l. 32: Maybe add some rough geographical location of the Ozark Plateau here, e.g., "central USA". Readers outside the US will not necessarily have heard of the Ozark Plateau or know in which part of the US Arkansas is.

l. 82: Was there a specific reason for testing flight capacity in a pairwise set-up? If so, please elaborate. If not, please discuss possible interactions leading to flight between the two specimens in the testing dish.

l. 150-157 and discussion: Since you have sexed the beetles in the study it would be interesting to discuss the sex-ration of flying beetles. You have provided this information in Table 1 but you could comment on it in the text as well.

Figure 3: Could be clearer. Instead of just showing the probabilities of survivorship according to the Kalan-Meier model, you could show and/or discuss the actual mortality in your experiment at the 24-hour intervals.

Author Response

Dear Journal Reviewer,

We greatly appreciate the expeditious review that improved the manuscript. Thank you for your time and improving our paper.

REVIEWER #1

The study described in the manuscript aims to assess the flight capacity and the response to drying of two species of Dytiscidae in an experimental set-up. The study is straightforward and well written. Due to the limited distributions of the species, the study could have important implications regarding the conservation of the beetles and their habitats.

I have just very few minor comments:

1. 31: Please add the year of publication behind the authority at first mentioning of the species: Heterosternuta sulphuria Matta and Wolfe, 1979; Heterosternuta phoebeae Wolfe and Harp, 2003

Author response: Dates were added following authorities of each species listed.

1. 32: Maybe add some rough geographical location of the Ozark Plateau here, e.g., "central USA". Readers outside the US will not necessarily have heard of the Ozark Plateau or know in which part of the US Arkansas is.

Author response: Added the highlighted section to this sentence “Heterosternuta sulphuria Matta and Wolfe, 1979 and Heterosternuta phoebeae Wolfe and Harp, 2003 are endemic predaceous diving beetles occurring in streams on the Ozark Plateau [1-3], located within the Interior Highlands in the mid-continental U.S.”

1. 82: Was there a specific reason for testing flight capacity in a pairwise set-up? If so, please elaborate. If not, please discuss possible interactions leading to flight between the two specimens in the testing dish.

Author response: While interactions among individuals in this setup could occur and potentially affect flight, we did not observe any apparently antagonsitic interactions and individuals were observed to move independently and typocally with miminal to zero contact between individuals.

1. 150-157 and discussion: Since you have sexed the beetles in the study it would be interesting to discuss the sex-ration of flying beetles. You have provided this information in Table 1 but you could comment on it in the text as well.

Author response: Added sentence to text at line 159: “Across sexes, approximately equal numbers of males and females were observed to fly (Table 1).”

Figure 3: Could be clearer. Instead of just showing the probabilities of survivorship according to the Kalan-Meier model, you could show and/or discuss the actual mortality in your experiment at the 24-hour intervals.

Author response: Data analyses simply focused on the Kalan-Meier model/statistics as given in the text and figure. A sentence was modified/added based on the reviewer recommendation: “Beetles in the drying treatment were observed to significantly decline after approximately 75 hours of drying, whereas little mortality was observed within 24 or 48 hours when the substrate still contained some moisture. Mortality reached 100% in the drying experiment after approximately three days when the sand substrate was completely dry. Zero beetles were observed to fly during the experiment from the open microcosms, across both drying and wet treatments.”

Reviewer 2 Report

This study examines flight capability in 2 predaceous diving beetle species in the genus Heterosternuta. Of these species, one occurs in perennial aquatic habitats that rarely dry whereas the other occurs in streams that can have periods of zero flow. Because of this, it was hypothesized that the species in the perennial habitats would have a lower capacity for dispersal via flying. This hypothesis was tested and confirmed with this study. 

This paper is well written and clearly presented. I only have a couple minor suggestions:

Line 38 (Page 1): "In addition to new distributional information for H. sulphuria, a total of six other hydroporine species were collected from historical surveys" - what are these species - I think your readers that know dytiscids would be interested.

Lines 142-144. The size measurements have no units, neither here nor the y-axes of Figure 2. These beetles are roughly between 3-5 mm in length, so I'm not sure what units would lead to measurement values in the 30s and 40s? Are they tenths of a millimeter? If they are tenths of a millimeter, perhaps change to millimeters by moving the decimal place? Whatever the units, they just need to be reported.

That's all I have. I enjoyed reading about the experiment and results.

Author Response

Dear Journal Reviewer,

We greatly appreciate the expeditious review that improved the manuscript. Thank you for your time and improving our paper.

 

REVIEWER #2

This study examines flight capability in 2 predaceous diving beetle species in the genus Heterosternuta. Of these species, one occurs in perennial aquatic habitats that rarely dry whereas the other occurs in streams that can have periods of zero flow. Because of this, it was hypothesized that the species in the perennial habitats would have a lower capacity for dispersal via flying. This hypothesis was tested and confirmed with this study. 

This paper is well written and clearly presented. I only have a couple minor suggestions:

Line 38 (Page 1): "In addition to new distributional information for H. sulphuria, a total of six other hydroporine species were collected from historical surveys" - what are these species - I think your readers that know dytiscids would be interested.

Author response: Appreciate the suggestion and added the following modifications to text: “Updated distributional records for H. sulphuria include 48 occurrences across 14 counties in northwestern Arkansas [3]. In addition to new distributional information for H. sulphuria, a total of six other hydroporines species were have been collected from historical surveys: Sanfilippodytes (sp.) Franciscolo, 1979; Hydrocolus (sp.) Roughley and Larson 2000, Heterosternuta wickhami Zaitzev 1908, H. ouachita Matta and Wolfe 1979; H. pulchra LeConte 1855; and H. phoebeae Wolfe and Harp 2003., one of which was the congener Among these, H. phoebeae [2], ] is also a species of greatest conservation need (SGCN) in Arkansas because of its narrow distribution across only a few counties [2,3].”

Lines 142-144. The size measurements have no units, neither here nor the y-axes of Figure 2. These beetles are roughly between 3-5 mm in length, so I'm not sure what units would lead to measurement values in the 30s and 40s? Are they tenths of a millimeter? If they are tenths of a millimeter, perhaps change to millimeters by moving the decimal place? Whatever the units, they just need to be reported.

Author response: Added the units to the Figure 2 caption: “(mm; y-axis, count of individuals; x-axis).”  Units (mm) were also added to the text at approx. line 148.

That's all I have. I enjoyed reading about the experiment and results.

Reviewer 3 Report

This manuscript investigated how two endemic Heterosternuta diving beetle species response to habitat drying. The study design is good, although it can be better if the morphological traits of the specimens used in the study could be collected to support some statements in Discussion. The paper is quite well-written, but it may need more references/data to support its statements. The figures are informative. In general, this is a good paper.

The country/countries of the authors' affiliations should be added. 

Line 32: Where is the Ozark Plateau located? Please add the state/province, and the country.

Lines 35-36: 'Updated distributional records for...' Please mention the year.

Lines 143-144: It is more scientific and informative to present mean values and the standard deviations of the body length and width, instead of mean values alone.

Line 193: '...disperse to new habitats This has...' A dot (.) is missing at the end of 'new habitats'.

Lines 197-199: Do the authors have any info about the morphology of flight muscles and hind wings of the study species? In the cited literature (Jackson 1952), the species are not under the genus Heterosternuta. Is it still possible for the authors to check the specimens of the beetles used in this study and record the morphological information of the hindwings and flight muscles?

Lines 202-204: Can the authors provide more relevant references to support this statement? The cited literature are not on diving beetles, which may have quite different traits than terrestrial Hemiptera studied in the cited literature.

Lines 244-248: It is better to mention the statement is only a hypothesis, which should be tested in future studies, because the authors did not provide any references to support such a statement.

Figure 2: The labels of x-axis are missing.

 

Some references that could be useful if the authors want to improve the manuscript to give a board vision on dytiscid conservation regarding dispersal and movement barriers:

Bilton, D. T. (2023). Dispersal in dytiscidae. In Ecology, systematics, and the natural history of predaceous diving beetles (Coleoptera: Dytiscidae) (pp. 505-528). Cham: Springer International Publishing.   Boda, P., & Csabai, Z. (2009). Seasonal and diel flight activity patterns of aquatic Coleoptera and Heteroptera. Internationale Vereinigung für theoretische und angewandte Limnologie: Verhandlungen, 30(8), 1271-1274.   Csabai, Z., Boda, P., Bernath, B., Kriska, G., & Horvath, G. (2006). A ‘polarisation sun‐dial’dictates the optimal time of day for dispersal by flying aquatic insects. Freshwater Biology, 51(7), 1341-1350.   Csabai, Z., Kálmán, Z., Szivák, I., & Boda, P. (2012). Diel flight behaviour and dispersal patterns of aquatic Coleoptera and Heteroptera species with special emphasis on the importance of seasons. Naturwissenschaften, 99, 751-765.   Davy-Bowker, J. (2002). A mark and recapture study of water beetles (Coleoptera: Dytiscidae) in a group of semi-permanent and temporary ponds. Aquatic Ecology, 36(3), 435-446.   Drotz, M. K., Brodin, T., Saura, A., & Giles, B. E. (2012). Ecotype differentiation in the face of gene flow within the diving beetle Agabus bipustulatus (Linnaeus, 1767) in northern Scandinavia. PLoS one, 7(2), e31381.   Iversen, L. L., Rannap, R., Thomsen, P. F., Kielgast, J., & Sand‐Jensen, K. (2013). How do low dispersal species establish large range sizes? The case of the water beetle Graphoderus bilineatus. Ecography, 36(7), 770-777.   Iversen, L. L., Rannap, R., Briggs, L., & Sand‐Jensen, K. (2017). Time‐restricted flight ability influences dispersal and colonization rates in a group of freshwater beetles. Ecology and Evolution, 7(3), 824-830.   Liao, W., Venn, S., & Niemelä, J. (2020). Environmental determinants of diving beetle assemblages (Coleoptera: Dytiscidae) in an urban landscape. Biodiversity and Conservation, 29(7), 2343-2359.   Liao, W., Venn, S., & Niemelä, J. (2022). Diving beetle (Coleoptera: Dytiscidae) community dissimilarity reveals how low landscape connectivity restricts the ecological value of urban ponds. Landscape Ecology, 37(4), 1049-1058.   Lundkvist, E., Landin, J., & Milberg, P. (2001). Diving beetle (Dytiscidae) assemblages along environmental gradients in an agricultural landscape in southeastern Sweden. Wetlands, 21(1), 48-58.   Lundkvist, E., Landin, J., & Karlsson, F. (2002, January). Dispersing diving beetles (Dytiscidae) in agricultural and urban landscapes in south-eastern Sweden. In Annales Zoologici Fennici (pp. 109-123). Finnish Zoological and Botanical Publishing Board.   Matsushima, R., & Yokoi, T. (2020). Flight capacities of three species of diving beetles (Coleoptera: Dytiscidae) estimated in a flight mill. Aquatic Insects, 41(4), 332-338.   Phillipsen, I. C., Kirk, E. H., Bogan, M. T., Mims, M. C., Olden, J. D., & Lytle, D. A. (2015). Dispersal ability and habitat requirements determine landscape‐level genetic patterns in desert aquatic insects. Molecular Ecology, 24(1), 54-69.   ZALOM, F. G., Grigarick, A. A., & WAY, M. O. (1980). Diel flight periodicities of some Dytiscidae (Coleoptera) associated with California rice paddies. Ecological Entomology, 5(2), 183-187.

Author Response

Dear Journal Reviewer,

We greatly appreciate the expeditious review that improved the manuscript. Thank you for your time and improving our paper.

REVIEWER #3

This manuscript investigated how two endemic Heterosternuta diving beetle species response to habitat drying. The study design is good, although it can be better if the morphological traits of the specimens used in the study could be collected to support some statements in Discussion. The paper is quite well-written, but it may need more references/data to support its statements. The figures are informative. In general, this is a good paper.

The country/countries of the authors' affiliations should be added. 

Line 32: Where is the Ozark Plateau located? Please add the state/province, and the country.

Author response: Improved this information with the following edits: Heterosternuta sulphuria Matta and Wolfe, 1979 and Heterosternuta phoebeae Wolfe and Harp, 2003 are endemic predaceous diving beetles occurring in streams on the Ozark Plateau [1-3], located within the Interior Highlands in the mid-continental U.S.

Lines 35-36: 'Updated distributional records for...' Please mention the year.

Author response: edited as follows: “. Updated distributional records for H. sulphuria in 2009 included 48 occurrences across 14 counties in northwestern Arkansas [3].”

Lines 143-144: It is more scientific and informative to present mean values and the standard deviations of the body length and width, instead of mean values alone.

Author response: This review statement is in agreement; We added the figure of length/width to show this variation, although we did not report it in the text.

Line 193: '...disperse to new habitats This has...' A dot (.) is missing at the end of 'new habitats'.

Author response: Added a period to the end of this sentence.

Lines 197-199: Do the authors have any info about the morphology of flight muscles and hind wings of the study species? In the cited literature (Jackson 1952), the species are not under the genus Heterosternuta. Is it still possible for the authors to check the specimens of the beetles used in this study and record the morphological information of the hindwings and flight muscles?

Authors response: While Jackson dissected some individuals to assess flight musculature, we did not perform that in this study. We preliminarily dissected some individuals and observed flight muscles, but after prolonged preservation it was difficult to discern microstructure. Both microstructure of wing musculature and wing morphometry in comparison with flight-capable congeners is another study that should be conducted using species found to be flightless and the numerous likely flight-capable hydroporines occupying less permanent waters.

Lines 202-204: Can the authors provide more relevant references to support this statement? The cited literature are not on diving beetles, which may have quite different traits than terrestrial Hemiptera studied in the cited literature.

Author response: Edited the text accordingly: Differences in body size between H. sulphuria and H. phoebeae are associated with flight capacity, since the former has a larger body and is also more capable of flight based on our observations. Some studies have demonstrated that increasing body size enhances flight ability for dispersal; among terrestrial insects, larger insects have been shown to contain more energy storage that enables longer flight durations and greater distances [8,9]. While variable sizes of hydrophilid water beetles persist among diverse aquatic habitats, the persistence and stability of habitats have been shown to drive dispersal in addition to differences in wing morphologies within species complexes [10]. Among diving beetles, dispersal is linked as well to habitat persistence and species’ ability to cope with changing environments [11] and this can be independent of body size, although to date relatively small hydroporines such as those tested in the current student have been shown to exhibit flightlessness [6, this study]. Moreover, the energetic cost of flight has been shown to decrease with increasing body size in some insects [12].

Added two citations/refs: Arribas, P.; Velasco, J.; Abellan, P.; Sanchez-Fernandez, D.; Andujar, C.; Calosi, P.; Millian, A.; Ribera, I.; Bilton, D.T. Dispersal ability rather than ecological tolerance drives differences in range size between lentic and lotic waterbodies (Coleoptera: Hydrophilidae). 2012. Journal of Biogeography, 39:984 – 994.  

Bilton, David T. "Dispersal in dytiscidae." Ecology, systematics, and the natural history of predaceous diving beetles (Coleoptera: Dytiscidae). Cham: Springer International Publishing, 2023. 505-528.

Lines 244-248: It is better to mention the statement is only a hypothesis, which should be tested in future studies, because the authors did not provide any references to support such a statement.

Author response: A good point. Changed accordingly: “In Britain, flightless water beetles are understood to migrate between populations via wet intervening regions [1718], including subsurface aquatic habitats. In our microcosm drying experiments, dying and dead individuals were mostly found head-down within the substrate and therefore it isit might be hypothesized possible that some individuals accidentally or purposely could enter groundwater systems and disperse to new locations.”

Figure 2: The labels of x-axis are missing. 

Author response: We clarified the axes in the figure by inserting the units of measurements within the figure caption, with short descriptions.

Some references that could be useful if the authors want to improve the manuscript to give a board vision on dytiscid conservation regarding dispersal and movement barriers:

Author Response: In this paper our primary focus was on the flight capacity of H. sulphuria. While there are numerous conservation implications for flightlessness across this fauna and aquatic habitats, we did not expand on these implications here. Perhaps another paper could focus on this topic while using these species as cases studies of specialized fauna. We did however add two additional citations involving flight of the Dytiscidae, lines 305-310.

 

Thank you to the three reviewers for reviewing the manuscript, which helped improve the manuscript. I look forward to submitting the revised manuscript for review.

Round 2

Reviewer 3 Report

The authors have put sufficient effort in the revision. I suggest the manuscript being accepted for publication.