Background

The evolution of the nervous system, especially the brain,is a key for animals to perceive and respond to the environment in which they live. Brain size has been found to be associated with morphological evolution. Large brains are associated with increased behavioral fexibility thus enabling animals to successfully cope with novel environmental challenges, and large brains are bene ficial for individuals under new selective regimes (Wyles et al. 1983; Sol and Lefebvre 2000; Sol et al. 2002; Healy and Rowe 2007). Because large brain size favors individuals when establishing in novel environments, it also increases the opportunities for allopatric speciation (Sol and Price 2008). Brain size was related to foraging innovations among species (Lefebvre et al. 1997). For example, brain size as a refection of cognitive skills accounted for the ability to cope with novel habitats (Sol et al. 2005).In addition, the northern distribution limits of birds are governed by the relative size of the hippocampus (Garamszegi and Lucas 2005). In birds, brain size is strongly positively correlated with head size (Møller 2010), but also with prey size and vocalizations, because individuals with large heads eat large food items and produce high frequency calls (Podos 2001; Podos et al. 2004).

Bite force is another important ecological trait of animals that may be tightly linked to both type and magnitude of the ecological challenges such as food acquisition,mate choice through effects on vocalizations, competition for access to mates and physical defense against predators (Anderson et al. 2008). A recent study revealed fast-evolving ecomorphological variation among populations of Lizard (Podarcis bocagei), where a direct association existed between head morphology and bite performance (Gomes et al. 2018). Therefore, both brain size and bite force are important traits for successful dispersal and colonization of novel environments.

Here we hypothesize that bird species with larger distribution ranges may have larger head size, and we test this by comparing head size in two sister species of parrotbills (Fig. 1) that differ considerably in distribution range (Fig. 2). These two sister species of parrotbills,Ashy-throated Parrotbill (Paradoxornis alphonsianus)and Vinous-throated Parrotbill (P. webbianus), both originate from the Himalayan area and have long been considered two subspecies of the same species (Delacour 1946). Recent studies also indicated that these two parrotbill species may be conspecific, and that they have diverged ca. 856,000 years ago, although substantial gene fow occurs after presumed secondary contact ca.290,000 years ago (Yeung et al. 2011; Shaner et al. 2015).Although these two parrotbills can be regarded either as sister species or distinct subspecies, their distribution ranges are significantly different with the Ashy-throated Parrotbill limited to the Himalayan area while the Vinous-throated Parrotbill has dispersed to northern and eastern China where it occupies a much larger area.Thus a comparison of morphology of these two species constitutes a unique opportunity for this study. We predicted that the Vinous-throated Parrotbill possesses a larger head size than does the Ashy-throated Parrotbill.Furthermore, bill size and bite force were also compared between these populations.

Fig. 2 The distribution ranges and sampling sites of two sister species of parrotbills in this study. For Vinous-throated Parrotbills, three geographic populations were sampled, including Guizhou, Jiangxi and Hebei whilst for Ashy-throated Parrotbills the Guizhou population was sampled

Fig. 1 The Vinous-throated Parrotbill (Paradoxornis webbianus) (a; photo by Naxun Zhao) and Ashy-throated Parrotbill (P. alphonsianus) (b; photo by Bruce Lyon)

Methods

Sampling and measurements

“Objective”表明该测试是一种客观评量，体现在各站测试目标明确，得分标准清楚；“Structured”意为测试的各站内容经过详尽的规划、非随机的测验，具有特定的目的性（即考查临床技能的某一特定部分，设计考试一定要有蓝图，见表1）；“Clinical”意为测验的是临床技能，而且使用真实的临床案例；“Examination”包含3层涵义，该测试同时可作为回馈性测验、总结性测验和执照考试。据此，OSCE可运用于教学、毕业生或新进人员评鉴及执照考试。

Three geographic populations of Vinous-throated Parrotbills and one population of Ashy-throated Parrotbills were sampled (Fig. 2). The sampling sites include Guizhou, Jiangxi, and Hebei provinces, which represent populations located in southwestern, central and northern China. The Vinous-throated Parrotbill is distributed in all three areas, whilst the Ashy-throated Parrotbill only occurs in a limited area in southwestern China. They are both residents and the distribution ranges of these two parrotbills overlap in southwestern China (Fig. 2).

We set up mist nests from April to July 2016 in shrub,which is the classical habitat for both species of parrotbills, then measured head length, head width, head height, commissural width and tomial length to the nearest 0.01 mm for calculating head size and bill size by using a digital caliper, body mass to the nearest 0.01 g with a digital scale and bite force to the nearest 0.01 N with a micro-signal collector (NBIT-DUD-2404A, NBIT Inc.,Nanjing, China) with a sensor probe (S2-200NHL-001).For each individual three values of bite force were measured, and maximal bite force was used to represent bite force (Anderson et al. 2008). Values of head length were obtained by measuring the length from the tip of the beak to the back of the head and then subtracting beak length.Head width was measured as the maximum value at the widest point at the back of the head whilst head height was measured as the maximum value from the top of the head to the bottom behind the jaw. Finally, head size was estimated as the product of these three dimensions and 4/3π to obtain the volume of a spheroid. For bill size, we calculated the grasp index as the product of commissural width and tomial length (Yang et al. 2015). Tomial length was determined from the commissural point at the corner of the mouth whilst the commissural width was the distance between the commissural points (Rohwer and Spaw 1988).

Statistical analyses

Generalized linear mixed model (GLMM) with a nested structure of populations nested within species was used to investigate the effect of species and the interaction between species and populations (species × populations)on head size or maximal bite force by controlling for body mass and sampling date. For the statistics of maximal bite force, bill size was also included as a control variable. Pearson correlation was used to test the relationship between head size and body mass, maximal bite force and body mass, or maximal bite force and head size. For the correlation between maximal bite force and head size,body mass was included as a control variable. Multiple comparisons among values of head size or maximal bite force of the four sampled parrotbill populations was conducted by using the method of Fisher’s least significant difference (LSD). All values are presented as mean ± SD.All statistics were performed in IBM SPSS 20.0 for Windows (IBM Inc., USA).

Results

In total 94 individual parrotbills were sampled, with similar sample sizes among different populations (Table 1).Head size was positively correlated with bill size(r = 0.528, df = 94, p ＜ 0.001, Pearson correlation). Head size differed significantly among populations (F = 8.53,df = 3, p ＜ 0.001, ANOVA), in which the Guizhou population of Vinous-throated Parrotbill had the largest value(2.06 ± 0.19 cm3) whilst the Ashy-throated Parrotbill had the smallest value (1.57 ± 0.15 cm3). Bill size and head size of the Guizhou population of Vinous-throated Parrotbill was larger than that of the other populations and Ashy-throated Parrotbills (p ＜ 0.001 for all, LSD test;Table 1; Fig. 3), while no statistical differences were detected among the other populations (Tables 1, 2).

语言是文化的载体，为了促进华裔青少年对中华文化的认同，帮助他们找到文化归属，必须大力发展华文教育。然而，在东南亚华人社会，由于老一辈华族逐渐作古、华文教育人才有限、教学方式落伍、教学方法不当、教学资金有限，虽然经过十多年的华文开放，华族子弟并没有在语言、思想、传统礼仪、族群精神上发生多少改变。

语义上具有普遍性的网络词语很可能进入规范的现代汉语中。例如“萌”，在网络上流行后，先后均在多种报刊的头条出现：“谁在稀里糊涂地卖萌”(2011年12月19日《世界新闻报》)，“厦门公安网上“卖萌” 专家提醒“卖萌”要有度”(2011年12月28日《广州日报》，“萌可萌 非常萌”(2012年1月3日《羊城晚报》)……可见“萌”的语义接受普遍性很强，不仅在民众中广为流行，就连官方也主动接近。所以笔者认为，“萌”进入规范的现代汉语的可能性很大。

Table 1 Descriptive values (mean ± SD) for Vinousthroated and Ashy-throated parrotbills obtained in this study

Vinous-throated Parrotbill Ashythroated Parrotbill Guizhou Jiangxi Hebei Guizhou Head size (cm3) 2.06 ± 0.19 1.65 ± 0.22 1.62 ± 0.12 1.57 ± 0.15 Maximal bite force (N)9.49 ± 2.91 11.94 ± 3.53 14.24 ± 4.80 9.58 ± 3.36 Body mass (g) 9.45 ± 0.70 8.86 ± 0.54 9.07 ± 0.68 8.94 ± 0.71 Bill size (mm2,grasp index)50.37 ± 3.98 43.79 ± 5.34 43.03 ± 4.75 43.03 ± 4.75 Sample size 25 24 21 24

Fig. 3 The head size and maximal bite force values of four geographic populations in two sister species of parrotbills. Box plots represent error bars, medians, and 5- and 95-percentiles

Discussion

Numerous studies have supported the idea that animals with larger brain size have more fexible behavior that allows them to deal with challenges of novel environments, and thus perform more effciently in terms of resource use (Sol and Price 2008). Morelli et al. (2018)also showed that generalist cuckoo species tend to occupy larger distribution ranges than more specialist species. Therefore, it is reasonable to speculate that individuals with larger head size are more fexible in behavior,which is beneficial for colonizing larger areas. Because brain size can be predicted from head size, since they arestrongly positively correlated (Møller 2010), head size in birds can be used as a representation of brain size. This occurs because birds are constrained in morphology from the extreme costs of fight that put a premium on mass reduction. As predicted, head size of Vinous-throated Parrotbills varies among geographic populations and was significantly larger than that of Ashy-throated Parrotbills.However, the Guizhou populations of Vinous-throated Parrotbills and Ashy-throated Parrotbills had the largest difference in head size. This result is surprising because these two populations are the phylogenetically closest among the two parrotbill species. Thus the contrast in head size should be expected to be the smallest compared to contrasts among other population. One possible explanation may be that selection is intense between the Guizhou populations of the two parrotbills compared to other populations. A recent study showed that interspecific competition strongly infuences the evolution of traits involved in resource use (Drury et al. 2018). The two parrotbill species studied here originated from the Himalayan area, where altitude varies considerably. Habitats with distinct altitude can lead to distinct specialization in morphology and life history (Lu et al. 2010; Yang et al. 2012). In Guizhou, Ashy-throated Parrotbills live in the highland while Vinous-throated Parrotbills live in the lowland (Shaner et al. 2015). Furthermore, human settlements are concentrated in the lowland. Therefore, the Vinous-throated Parrotbill that disperses to new habitats(i.e. lowland with human settlement) may face challengesthat can be more readily resolved with a larger brain. Previous studies indicated that large brains and associated behavioral fexibility increase speciation rates (Nicolakakis et al. 2003; Ricklefs 2004), and parrotbill individuals that colonize new habitats may favor speciation. However, there are no differences in head size between the Ashy-throated Parrotbill and allopatric populations of Vinous-throated Parrotbill (Jiangxi and Hebei), which provides further evidence for the hypothesis that differences in head size found in the Guizhou populations of the two species are probably the result of local adaptation and are not species-specific.

Table 2 Multiple comparisons among different populations in two sister species of parrotbills by LSD method

NS: p ＞ 0.05; *0.01 ＜ p ＜ 0.05; **p ＜ 0.01

Vinous-throated Parrotbill Ashythroated Parrotbill Guizhou Jiangxi Hebei Guizhou Head size Vinous-throated Parrotbill Guizhou – ** ** **Jiangxi**–NSNS Hebei** NS–NS Ashy-throated Parrotbill Guizhou ** NS NS –Maximum bite force Vinous-throated Parrotbill Guizhou – * ** NS Jiangxi* –**Hebei** *–**Ashy-throated Parrotbill Guizhou NS * ** –

Table 3 The results of generalized linear mixed models (GLMM) with nested structure of populations nested in species for testing the predictors (species and the interaction between species and population) of the target measurements (head size or maximal bite force)

*GLMM was performed by controlling for body mass and sampling date **GLMM was performed by controlling for body mass, sampling date and bill size

?

A recent study revealed fast-evolving ecomorphological variation among populations of Lizards (Podarcis bocagei), where a direct association existed between head morphology and bite performance (Gomes et al. 2018).We investigated differences in bill size and bite force among populations, but the results showed the opposite tendency. The Guizhou population of Ashy-throated Parrotbills is smaller than the Jiangxi and Hebei populations,but not the Guizhou population of Vinous-throated Parrotbills. Variation among populations of Vinous-throated Parrotbills in bite force shows the opposite tendency compared to those for head size and bill size. In other words, the Guizhou populations of the two parrotbill species differed considerably in head size and bill size but not in bite force. Additionally, the tendency of variation in bite force is opposite to those for head size and bill size with populations with larger head size and bill size having weaker bite force. One possible explanation for this pattern is that populations with larger head size have larger bill size as a byproduct. Previous work showed a positive relationship between bill size and acoustic frequencies during song production (Podos 2001; Podos et al. 2004).The upper and lower mandibles of a larger bill may be more diffcult to stretch out and draw back by muscles,thus leading to a smaller bite force. This logical assumption is supported because head size was found to be positively correlated with bill size. Finally, variation in bite force among different populations of Vinous-throated Parrotbill may simply refect geographic variation in food resources, because larger beaks and larger bite force should allow for exploitation of larger and more variable food size (e.g. Lefebvre et al. 1997; Gomes et al. 2018),although this assumption needs further study.

In summary, this study supports the prediction that a larger head leads to more fexible behaviors that may be beneficial for parrotbills to utilize variable resources and thus contribute to their colonization of new habitats. Our study may therefore have implications and perspectives for the role of head size, and by implication brain size, in dispersal and adaptation in birds.

随着时代的发展木结构在房屋建造中得到广泛应用，同时也是一个普遍的应用领域。随着人们生活质量的提高，木结构建筑需求逐渐增加，其建筑数量逐渐加剧。

Conclusions

We showed that there are no differences in head size between the Ashy-throated Parrotbill and allopatric populations of the Vinous-throated Parrotbill, which provides evidence for the hypothesis that differences in head size found in the Guizhou populations of the two sister species are probably the result of local adaptation and are not species-specific. Our study has implications for avian dispersal and adaption related to head size such as diet ecology and vocalizations.

虽然系统功能学派对名物化的语篇功能展开了不少有意义的探索，但与词汇语法层面的研究相比还十分不足，在研究视角的广度和深度上还有待进一步拓展。为了更好地把握语篇层面名物化现象研究的现状、研究热点和未来的研究方向，本文拟通过运用知识图谱分析软件“引文空间”(CiteSpace)，对比分析国内外核心期刊近20年来发表的文献，全面考察国内外学界对英语名物化现象研究的趋势，以期为今后英语语篇名物化现象的研究提供参考。

Authors’ contributions

1 Ministry of Education Key Laboratory for Ecology of Tropical Islands, College of Life Sciences, Hainan Normal University, Haikou 571158, China. 2 Ecologie Systématique Evolution, Université Paris-Sud, CNRS, AgroParisTech, Université Paris-Saclay, 91405 Orsay Cedex, France.

Author details

WL and CY conceived and designed the experiment, XR, LM and JZ conducted the experiments and collectedfield data. APM provided new ideas for this manuscript. CY and XR performed data analyses and wrote the manuscript. WL and APM revised and improved the manuscript. All authors read and approved thefinal version of the manuscript.

We made GLMMs that control for body mass and sampling date in head size comparison and body mass,sampling date and head size in maximal bite force. The resulting comparisons showed that both species and the interaction between species and populations were significant predictors of head size (species: F1,90 = 23.76,p ＜ 0.001; species × populations: F2,90 = 71.03, p ＜ 0.001,GLMM). That also applied to maximal bite force (species: F1,90 = 23.34, p ＜ 0.001; species × populations:F2,90 = 28.55, p ＜ 0.001, GLMM) (Table 3). Finally, head size was positively correlated with body mass (r = 0.304,df = 94, p = 0.003; Pearson correlation) whilst maximal bite force was not significantly correlated with either body mass (r = ‒0.172, df = 94, p = 0.097, Pearson correlation) or head size after controlling for body mass(r = ‒0.131, df = 94, p = 0.210, Pearson correlation).

如今，复盘犯过的错和走过的弯路，我却不得不承认——对于创业者来说，华为的狼性文化在某种程度上非常值得借鉴和学习。

Not applicable.

We are grateful to two anonymous reviewers for providing constructive and valuable comments that significantly improved the quality of the manuscript.

Competing interests

The authors declare that they have no competing interests.

Availability of data and materials

The datasets used in the present study are available from the corresponding author on reasonable request.

This work was supported by the National Natural Science Foundation of China(Nos. 31272328, 31472013 and 31772453 to WL, and 31672303 to CY).

Acknowledgements

Ethics approval and consent to participate

The experiments comply with the current laws of China in which they were performed. Experimental procedures were in agreement with the Animal Research Ethics Committee of Hainan Provincial Education Centre for Ecology and Environment, Hainan Normal University (Permit No. HECEE-2012-003).

基本的Elman神经网络[12]由于承接层的存在，因此具有更强的记忆功能，这是与传统网络相比的优势所在。Elman网络中延迟单元的存在，使得Elman网络具有较强的泛化能力，对时间序列预测问题具有很好的解决能力。网络结构形式如图1所示，Y(k)、X(n)、U(k-1)分别是网络输入层、隐藏层和输出层。缺点是输入层、隐含层、神经元的准确选取往往要经过多次测试才能得到较合理的选值，且参数选取一定程度上具有的主观性，有时预测结果会发生失真现象。

Funding

米芾是历史上伟大的书法家，且在官场上清正廉洁、秉公执法，然而却因脾气古怪、放荡不羁，被人送外号“米癫”“米疯子”。

Consent for publication

References

Anderson RA, McBrayer LD, Herrel A. Bite force in vertebrates: opportunities and caveats for use of a nonpareil whole-animal performance measure.Biol J Linn Soc. 2008;93:709–20.

Delacour J. Les timaliinèes. L’Oiseau. 1946;16:7–36.

Drury JP, Tobias JA, Burns KJ, Mason NA, Shultz AJ, Morlon H. Contrasting impacts of competition on ecological and social trait evolution in songbirds. PLoS Biol. 2018;16:e2003563.

Garamszegi LZ, Lucas JR. Continental variation in relative hippocampal volume in birds: the phylogenetic extent of the effect and the potential role of winter temperatures. Biol Lett. 2005;1:330–3.

Gomes V, Carretero MA, Kaliontzopoulou A. Run for your life, but bite for your rights? How interactions between natural and sexual selection shape functional morphology across habitats. Sci Nat. 2018;105:9.

Healy SD, Rowe C. A critique of comparative studies of brain size. Proc R Soc B.2007;274:453–64.

Lefebvre L, Whittle P, Lascaris E, Finkelstein A. Feeding innovations and forebrain size in birds. Anim Behav. 1997;53:549–60.

Lu X, Yu T, Liang W, Yang C. Comparative breeding ecology of two whitebellied redstart populations at different altitudes. J Field Ornithol.2010;81:167–75.

Møller AP. Brain size, head size and behaviour of a passerine bird. J Evol Biol.2010;23:625–35.

Morelli F, Benedetti Y, Møller AP, Liang W, Carrascal LM. Cuckoos host range is associated positively with distribution range and negatively with evolutionary uniqueness. J Anim Ecol. 2018. https://doi.org/10.1111/1365-2656.12797.

Nicolakakis N, Sol D, Lefebvre L. Behavioural fl exibility predicts species richness in birds, but not extinction risk. Anim Behav. 2003;65:445–52.

Podos J. Correlated evolution of morphology and vocal signal structure in Darwin’sfinches. Nature. 2001;409:185–8.

Podos J, Southall JA, Marcos R, Rossi-Santos MR. Vocal mechanics in Darwin’sfinches: correlation of beak gape and song frequency. J Exp Biol.2004;207:607–19.

Ricklefs RE. Cladogenesis and morphological diversification in passerine birds.Nature. 2004;430:338–41.

Rohwer S, Spaw CD. Evolutionary lag versus bill-size constraints: a comparative study of the acceptance of cowbird eggs by old hosts. Evol Ecol.1988;2:27–36.

Shaner PJL, Tsao TH, Lin RC, Liang W, Yeh CF, Yang XJ, Lei F, Zhou F, Yang C,Hung LM, Hsu YC, Li SH. Climate niche differentiation between two passerines despite ongoing gene fl ow. J Anim Ecol. 2015;84:829–39.

Sol D, Duncan RP, Blackburn TM, Cassey P, Lefebvre L. Big brains, enhanced cognition, and response of birds to novel environments. Proc Natl Acad Sci USA. 2005;102:5460–5.

Sol D, Lefebvre L. Behavioural fl exibility predicts invasion success in birds introduced to New Zealand. Oikos. 2000;90:599–605.

Sol D, Price TD. Brain size and the diversification of body size in birds. Am Nat.2008;172:170–7.

Sol D, Timmermans S, Lefebvre L. Behavioural fl exibility and invasion success in birds. Anim Behav. 2002;63:495–502.

Wyles JS, Kunkel JG, Wilson AC. Birds, behavior and anatomical evolution. Proc Natl Acad Sci USA. 1983;80:4394–7.

Yang C, Liang W, Cai Y, Wu J, Shi S, Antonov A. Variation in russet sparrow (Passer cinnamomeus) breeding biology in relation to small-scale altitudinal differences in China. Zool Sci. 2012;29:419–22.

Yang C, Wang L, Cheng SJ, Hsu YC, Stokke BG, Røskaft E, Moksnes A, Liang W,Møller AP. Deficiency in egg rejection in a host species as a response to the absence of brood parasitism. Behav Ecol. 2015;26:406–15.

Yeung CKL, Lin RC, Lei F, Robson C, Hung LM, Liang W, Zhou F, Han L, Li SH,Yang X. Beyond a morphological paradox: complicated phylogenetic relationships of the parrotbills (Paradoxornithidae, Aves). Mol Phylogenet Evol. 2011;61:192–202.